learners preferred systems that collapse the second and third person categories to alternative homophony patterns. When 2+3 homophony was not available to participants (Condition 1), there was no stable pattern of responses: some participants used the same form for first and second persons, some used the same form for first and third, and some alternated randomly between the two.

This result is in direct contrast to the prediction we derived from Harley and Ritter’s (2002) theory. This theory is designed to derive 1+2 homophony, and *not* 2+3 homophony. Further, it does not distinguish 2+3 from 1+3 homophony. Ackema and Neeleman’s (2018) theory fares slightly better, as it posits that second and third person form a natural class (DIST) that excludes first person. This predicts that 2+3 homophony patterns should be preferred over 1+3 patterns, in accordance with our results (Forchheimer 1953, Bobaljik 2008; see also binary-features accounts). However, by also positing a feature shared between first and second person (PROX), this theory predicts an asymmetry between 1+2 and 1+3 homophony, not attested in our findings (similar predictions are made by Harbour (2016)). Thus, while the pattern of results in our experiment is quite clear, it does not straightforwardly match the predictions of either account.

Our results, however, do mirror what one might deem the most obvious typological asymmetry in figure 7: paradigms featuring 2+3 homophony are the most common (see table 9). Interestingly, an analogous pattern is found in the distribution of person systems across sign languages, where second and third person are consistently homophonous both in pointing signs and in other grammatical constructions (Meier 1990, Neidle et al. 2000), as well as in the spatial deixis domain in languages across both modalities: most locative systems (e.g., *here/there* in English) rely on a distinction between spaces in the vicinity of the speaker (1) and spaces not in the vicinity of the speaker (2+3) (Harbour 2016).<fnref n="25" /> This match between our results and typology suggests the possibility that some additional force is at play, which distinguishes first and second person, even if they do form a natural class.<fnref n="26" />

To summarize, recall that at issue here was the special status of the [±participant] distinction in driving homophony. Theories based on the traditional set of binary features, like Harley and Ritter’s (2002), are designed to capture this particular natural class, thus predicting systematic

<footnote n="25">²⁵ In principle, the English-speaking participants in our experiments might be extrapolating their experience with the locatives *here* and *there*, which make a 2+3 partition of the space, to the person space (Daniel Harbour, pers. comm.). However, in our view this would be rather surprising.</footnote>

<footnote n="26">²⁶ It is worth briefly discussing two alternative interpretations of our experimental results. First, it could be that the little sister was treated as a speech act participant rather than as a third person referent—for example, because she is spatially close to the speaker and hearer in the illustrations (Peter Ackema, pers. comm.). To address this possibility, we reran one condition of this experiment with a different set of images where the little sister was seated in the background together with the parents. The results replicate the findings reported here, suggesting this is not an issue (see the online appendix, figure A.3). Second, participants might think the speaker (the girl with the hat) is in some cases directly addressing the others (e.g., parents) instead of the intended hearer (the girl asking the questions). If an addressee shift of this sort were at play, there would be no “true” third person, explaining why participants derive what seems to be a 2+3 pattern (as suggested by Klaus Abels, pers. comm.). However, in the postexperiment debrief, where participants had to provide meanings for each of the words they had learned, most participants (across all three conditions) described the pronominal form they used to refer to nonparticipants in the conversation (e.g., the parents) as meaning *them* in English. This shows that they were representing one of the pronominal forms as a true third person, and did not interpret the speaker as directly addressing the others.</footnote>
homophony between speech act participants, that is, first and second person. Our results do not bear this out. Rather, behavior appears to be consistent with a preference to distinguish the speaker from others: person systems that distinguish between participants and nonparticipants—making use of the PROX or [±participant] feature—seem to be dispreferred over systems that make use of the DIST or [±speaker] feature. The preference for 2+3 systems in our experiment might then lie in participants’ unwillingness to lose a distinction they have learned between forms that include and forms that exclude the speaker.<fnref n="27" /> This bias for speaker distinctiveness was partly discussed in the context of Zwicky’s generalization and Experiment 2 above. We therefore return to this issue in the next section.

## 5 General Discussion

The main aim of the experiments reported here was to bring behavioral evidence from learning to bear on how person systems are represented and whether they are subject to universal constraints on possible partitions. We see our results as making three main contributions: (a) we provide confirmatory evidence that the person space is represented in terms of primitive features, (b) we point to the need for restrictions on patterns of inclusive homophony based on weak biases rather than hard-and-fast constraints, (c) we provide new evidence for an asymmetry between 2+3 and other two-way homophony patterns involving 1 (EXCL+INCL), 2, and 3 person categories. We first summarize each of these in turn and then discuss a number of broader issues raised by our results as a whole.

In Experiment 1, we sought to provide evidence that the person space is represented as an interacting set of universal features. While this idea forms the basis of most theories of person in the theoretical linguistics literature, to date the link with learnability has been left implicit. However, these theories make testable predictions. If learners represent the person space as the interaction of a (primitive) set of person features, then categories that form a natural class should be readily mapped to the same phonological form (as formalized in Pertsova 2011, among many others). The learner must simply determine which feature(s) are underspecified. A set of cells that cannot be characterized as constituting a natural class arguably requires learners to first learn the different categories (i.e., as feature bundles) and then independently learn to map the relevant set to a phonological form. Thus, a feature-based theory of the person space predicts that paradigms with this kind of random homophony should be less readily learned than homophony among meanings with a shared feature. By contrast, if learners perceive the person space as a simple conjunction of four person categories (first, inclusive, second, and third), then there is no basis for predicting that some homophony patterns should be more learnable than others.

The predictions of feature-based approaches to person were borne out in Experiment 1: homophony patterns among forms sharing a feature were indeed easier to learn and were more

<footnote n="27">²⁷ The extrapolation paradigm we use is designed to target precisely this kind of effect. An ease-of-learning design, by contrast, may be more likely to tap purely into learners’ perceptions of how natural it is for two categories (e.g., first and second persons) to share a form. For some evidence suggesting this, see https://osf.io/9nc36/?view_only=09b7115978e14ae0898d4b8fb47fb4b6.</footnote>
homophony between speech act participants, that is, first and second person. Our results do not bear this out. Rather, behavior appears to be consistent with a preference to distinguish the speaker from others: person systems that distinguish between participants and nonparticipants—making use of the PROX or [±participant] feature—seem to be dispreferred over systems that make use of the DIST or [±speaker] feature. The preference for 2+3 systems in our experiment might then lie in participants’ unwillingness to lose a distinction they have learned between forms that include and forms that exclude the speaker.<fnref n="27" /> This bias for speaker distinctiveness was partly discussed in the context of Zwicky’s generalization and Experiment 2 above. We therefore return to this issue in the next section.

## 5 General Discussion

The main aim of the experiments reported here was to bring behavioral evidence from learning to bear on how person systems are represented and whether they are subject to universal constraints on possible partitions. We see our results as making three main contributions: (a) we provide confirmatory evidence that the person space is represented in terms of primitive features, (b) we point to the need for restrictions on patterns of inclusive homophony based on weak biases rather than hard-and-fast constraints, (c) we provide new evidence for an asymmetry between 2+3 and other two-way homophony patterns involving 1 (EXCL+INCL), 2, and 3 person categories. We first summarize each of these in turn and then discuss a number of broader issues raised by our results as a whole.

In Experiment 1, we sought to provide evidence that the person space is represented as an interacting set of universal features. While this idea forms the basis of most theories of person in the theoretical linguistics literature, to date the link with learnability has been left implicit. However, these theories make testable predictions. If learners represent the person space as the interaction of a (primitive) set of person features, then categories that form a natural class should be readily mapped to the same phonological form (as formalized in Pertsova 2011, among many others). The learner must simply determine which feature(s) are underspecified. A set of cells that cannot be characterized as constituting a natural class arguably requires learners to first learn the different categories (i.e., as feature bundles) and then independently learn to map the relevant set to a phonological form. Thus, a feature-based theory of the person space predicts that paradigms with this kind of random homophony should be less readily learned than homophony among meanings with a shared feature. By contrast, if learners perceive the person space as a simple conjunction of four person categories (first, inclusive, second, and third), then there is no basis for predicting that some homophony patterns should be more learnable than others.

The predictions of feature-based approaches to person were borne out in Experiment 1: homophony patterns among forms sharing a feature were indeed easier to learn and were more

<footnote n="27">²⁷ The extrapolation paradigm we use is designed to target precisely this kind of effect. An ease-of-learning design, by contrast, may be more likely to tap purely into learners’ perceptions of how natural it is for two categories (e.g., first and second persons) to share a form. For some evidence suggesting this, see https://osf.io/9nc36/?view_only=09b7115978e14ae0898d4b8fb47fb4b6.</footnote>
likely to be inferred when extrapolating a known form to a new meaning. This was the case even though the specific features involved are not active in the participants' native language, suggesting that this is how these systems are represented. These findings draw an obvious parallel with work in phonology showing that rules that can be characterized on the basis of features (or natural classes) are easier to learn than rules that group together a set of featurally distinct segments (e.g., Saffran and Thiessen 2003, Cristià and Seidl 2008, Moreton and Pater 2012). This suggests that feature-based representations are relevant for learning across domains, although the set of relevant features is of course domain-specific.

In Experiment 2, we turned to Zwicky's (1977) well-known observation that person partitions without an inclusive distinction assimilate inclusive with first person (rather than second or third). Different approaches to person treat this apparently strong asymmetry differently. Harbour's (2016) and Ackema and Neeleman's (2018) theories are purpose-built to derive first-inclusive tripartitions only (though Ackema and Neeleman's may also be able to generate second-inclusive homophony).<fnref n="28" /> However, approaches like Harley and Ritter's (2002) can derive both first-inclusive and second-inclusive (though the latter is more marked).

Again, translating the predictions of these theories in terms of learnability, we tested whether homophony of inclusive with first, second, or third person was treated distinctly by learners. We found that third-inclusive homophony was particularly problematic, while first-inclusive had only a weak advantage over second-inclusive. In accordance with Harley and Ritter's (2002) theory, this suggests that there is no hard constraint against systems that systematically collapse second and inclusive persons; rather, inclusive can form a natural class with both first and second person, though not (readily) with third.

Finally, in Experiment 3 we provided new evidence for a learning-based asymmetry between partitions with homophony between second and third person (2+3) on the one hand, and both first-second (1+2) and first-third (1+3) homophony patterns on the other. While the former were readily inferred by our participants, the latter were not. This result roughly matches an asymmetry found in the typological distribution of pronominal systems. However, it is problematic under the assumption that all homophony patterns targeting meanings that share a feature should be equally possible. Indeed, theories like Harley and Ritter's (2002), which posit that first and second person form a salient natural class—of speech act participants—would predict that 1+2 homophony should if anything have a learnability advantage. Alternative approaches such as Harbour's (2016) and Ackema and Neeleman's (2018) posit common features between both first and second categories, and between second and third; therefore, their most straightforward prediction is a specific learnability disadvantage for 1+3 homophony. Participants in Experiment 3 instead consistently inferred 2+3 homophony whenever this was consistent with the input they were trained on, while 1+2 and 1+3 were equally dispreferred.

<footnote n="28">²⁸ Ackema and Neeleman's (2018) system does derive second-inclusive systems (violating Zwicky's generalization) whenever (a) *PROX* and *PROX-PROX* have different phonological realizations, and (b) there is an impoverishment of *DIST* in the plural when it is a dependent of *PROX*.</footnote>
likely to be inferred when extrapolating a known form to a new meaning. This was the case even though the specific features involved are not active in the participants' native language, suggesting that this is how these systems are represented. These findings draw an obvious parallel with work in phonology showing that rules that can be characterized on the basis of features (or natural classes) are easier to learn than rules that group together a set of featurally distinct segments (e.g., Saffran and Thiessen 2003, Cristià and Seidl 2008, Moreton and Pater 2012). This suggests that feature-based representations are relevant for learning across domains, although the set of relevant features is of course domain-specific.

In Experiment 2, we turned to Zwicky's (1977) well-known observation that person partitions without an inclusive distinction assimilate inclusive with first person (rather than second or third). Different approaches to person treat this apparently strong asymmetry differently. Harbour's (2016) and Ackema and Neeleman's (2018) theories are purpose-built to derive first-inclusive tripartitions only (though Ackema and Neeleman's may also be able to generate second-inclusive homophony).<fnref n="28" /> However, approaches like Harley and Ritter's (2002) can derive both first-inclusive and second-inclusive (though the latter is more marked).

Again, translating the predictions of these theories in terms of learnability, we tested whether homophony of inclusive with first, second, or third person was treated distinctly by learners. We found that third-inclusive homophony was particularly problematic, while first-inclusive had only a weak advantage over second-inclusive. In accordance with Harley and Ritter's (2002) theory, this suggests that there is no hard constraint against systems that systematically collapse second and inclusive persons; rather, inclusive can form a natural class with both first and second person, though not (readily) with third.

Finally, in Experiment 3 we provided new evidence for a learning-based asymmetry between partitions with homophony between second and third person (2+3) on the one hand, and both first-second (1+2) and first-third (1+3) homophony patterns on the other. While the former were readily inferred by our participants, the latter were not. This result roughly matches an asymmetry found in the typological distribution of pronominal systems. However, it is problematic under the assumption that all homophony patterns targeting meanings that share a feature should be equally possible. Indeed, theories like Harley and Ritter's (2002), which posit that first and second person form a salient natural class—of speech act participants—would predict that 1+2 homophony should if anything have a learnability advantage. Alternative approaches such as Harbour's (2016) and Ackema and Neeleman's (2018) posit common features between both first and second categories, and between second and third; therefore, their most straightforward prediction is a specific learnability disadvantage for 1+3 homophony. Participants in Experiment 3 instead consistently inferred 2+3 homophony whenever this was consistent with the input they were trained on, while 1+2 and 1+3 were equally dispreferred.

<footnote n="28">²⁸ Ackema and Neeleman's (2018) system does derive second-inclusive systems (violating Zwicky's generalization) whenever (a) *PROX* and *PROX-PROX* have different phonological realizations, and (b) there is an impoverishment of *DIST* in the plural when it is a dependent of *PROX*.</footnote>
To summarize, our results suggest that learners represent the person space in units that are smaller than person categories (features) and that instantiate natural classes. Natural-class-based similarity therefore clearly plays an important role in determining how humans partition this person space. Indeed, a bias toward patterns based on natural class similarity pushes learners to preferentially collapse categories that share features (when they are required to do so). Our results support the claim that inclusive and second person should be included in the set of natural classes in this domain. However, there is also reason to believe that a bias for keeping the speaker distinct may also be at play. Indeed, our findings are compatible with the idea that natural-class-based similarity, and speaker- (or ego-)based distinctiveness may be two independent forces influencing the learnability of person systems. In Experiment 2, the partition characterized by first-inclusive homophony was learned most readily and is consistent with both of these pressures: it involves homophony among meanings that share a feature, [+speaker] *and* keeps person categories implicating the speaker distinct from other categories. The second-inclusive homophony pattern is the next best, involving homophony among shared meanings but not maintaining speaker categories as distinct from others. In Experiment 3, these two pressures led learners to infer 2+3 whenever they could—again among the options presented to learners in this case, 2+3 homophony is the only one to involve both categories that are highly similar and forms that keep the speaker category distinct. The fit is not perfect: in principle, as noted above, we might have expected the first-inclusive advantage to be stronger, and 1+2 homophony to be preferred over 1+3. One possibility is that our failure to find these differences might be the result of particular features of our experimental design. For example, a difference in learnability between 1+2 and 1+3 might be revealed in an ease-of-learning experiment (see Experiment 2), where resorting to the preferred 2+3 pattern is not possible.

In our discussion of Experiment 2, we suggested that a speaker distinctiveness bias may be the result of the cognitive importance of the ego (see Dixon 1994). Indeed, research on early pronoun acquisition has argued for an egocentric bias, whereby children perceive the world as a function of their presence in it and adopt categorization systems that carry this distinction (Charney 1980, Loveland 1984, Moyer et al. 2015). This is also supported by the fact that perspective-taking appears to be a capacity that takes time to develop; infants and young children do not always succeed on so-called theory-of-mind tasks that require them to recognize that their internal knowledge states are not the same as other people's (see, e.g., Ruffman 2014). If the pressure for keeping the speaker distinct in pronoun systems comes from a general egocentric bias, then we might expect (a) the bias to be stronger in children, and (b) the bias to be stronger when learners are active speakers of the language. The experiments reported here of course involved adults, and our participants were never themselves the speaker. However, further research could test both predictions.

An alternative is to build a speaker-based asymmetry between natural classes directly into a theory of person—at the same level of representation as the domain-specific primitive features. In a nutshell, the idea would be that the natural class “speaker” is somehow represented as special within the person space. The pressure for speaker distinctiveness would then be a special type of natural-class-based similarity that comes not directly from the set of primitive features but
To summarize, our results suggest that learners represent the person space in units that are smaller than person categories (features) and that instantiate natural classes. Natural-class-based similarity therefore clearly plays an important role in determining how humans partition this person space. Indeed, a bias toward patterns based on natural class similarity pushes learners to preferentially collapse categories that share features (when they are required to do so). Our results support the claim that inclusive and second person should be included in the set of natural classes in this domain. However, there is also reason to believe that a bias for keeping the speaker distinct may also be at play. Indeed, our findings are compatible with the idea that natural-class-based similarity, and speaker- (or ego-)based distinctiveness may be two independent forces influencing the learnability of person systems. In Experiment 2, the partition characterized by first-inclusive homophony was learned most readily and is consistent with both of these pressures: it involves homophony among meanings that share a feature, [+speaker] *and* keeps person categories implicating the speaker distinct from other categories. The second-inclusive homophony pattern is the next best, involving homophony among shared meanings but not maintaining speaker categories as distinct from others. In Experiment 3, these two pressures led learners to infer 2+3 whenever they could—again among the options presented to learners in this case, 2+3 homophony is the only one to involve both categories that are highly similar and forms that keep the speaker category distinct. The fit is not perfect: in principle, as noted above, we might have expected the first-inclusive advantage to be stronger, and 1+2 homophony to be preferred over 1+3. One possibility is that our failure to find these differences might be the result of particular features of our experimental design. For example, a difference in learnability between 1+2 and 1+3 might be revealed in an ease-of-learning experiment (see Experiment 2), where resorting to the preferred 2+3 pattern is not possible.

In our discussion of Experiment 2, we suggested that a speaker distinctiveness bias may be the result of the cognitive importance of the ego (see Dixon 1994). Indeed, research on early pronoun acquisition has argued for an egocentric bias, whereby children perceive the world as a function of their presence in it and adopt categorization systems that carry this distinction (Charney 1980, Loveland 1984, Moyer et al. 2015). This is also supported by the fact that perspective-taking appears to be a capacity that takes time to develop; infants and young children do not always succeed on so-called theory-of-mind tasks that require them to recognize that their internal knowledge states are not the same as other people's (see, e.g., Ruffman 2014). If the pressure for keeping the speaker distinct in pronoun systems comes from a general egocentric bias, then we might expect (a) the bias to be stronger in children, and (b) the bias to be stronger when learners are active speakers of the language. The experiments reported here of course involved adults, and our participants were never themselves the speaker. However, further research could test both predictions.

An alternative is to build a speaker-based asymmetry between natural classes directly into a theory of person—at the same level of representation as the domain-specific primitive features. In a nutshell, the idea would be that the natural class “speaker” is somehow represented as special within the person space. The pressure for speaker distinctiveness would then be a special type of natural-class-based similarity that comes not directly from the set of primitive features but
from the particular status of the speaker feature. This sketch is very speculative, and a worked-
out implementation is beyond the scope of this article. However, this idea is in the spirit of
Harbour (2016) and Ackema and Neeleman (2018), whose theories encode an inherent asymmetry
between speaker and addressee, built into the ontology (see footnote 15). Crucially, we would
argue that this asymmetry should be treated as a bias, which shapes but does not strictly delimit
the space of possible partitions.

Before moving on, we should mention an anonymous reviewer's concerns about whether our results could be accommodated by a non-feature-based approach to person. This is a sensible worry, as it questions whether our approach truly provides evidence that the person space is represented in terms of a set of universal primitives. To address this concern, let us say a few words about whether the results reported here are compatible with putative nonfeatural representations of the person space.

Our experiments show that learners are sensitive to whether certain semantic values (e.g., speaker, addressee) are included in the pronominal reference, regardless of the specific person category. This suggests that person categories form natural classes along these semantic dimensions. Here, we have treated these natural classes as defined by primitive features. Arguably, an alternative, non-feature-based approach would be one that does not decompose person categories into smaller units, but treats them as primitives themselves; for example, first, inclusive, second, and third would be four different primitives, as well as all other plural combinations (see Cysouw 2007 for discussion). We see a problem with this type of alternative view: in order to account for our main findings, this approach would need to explain why it is that learners are more likely to collapse some person categories than others, even when these categories are nonnative.

As a response to this issue, the same reviewer conjectures that some additional pragmatic
mechanism might result in more accurate learning predictions. For the time being, however, we
remain agnostic about how this proposal could be further developed into a full theory of person
that accounts for our results (and for the typology). Instead, we maintain that, to the extent that
learners are shown to be sensitive to the semantic overlap between categories, a feature-based
account of our results is more parsimonious (as well as in line with already established theories
of person).

6 Conclusion

Person systems have been extensively explored from a theoretical standpoint: a number of ap-
proaches have been proposed, each of which constrains the set of possible person partitions that
humans can represent, with the aim of explaining the prevalence of certain partitions of the person
space crosslinguistically. The experiments reported here inform these theoretical approaches by
generating direct behavioral evidence for the impact of hypothesized representations and con-
straints on the learnability of different person partitions. Indeed, our results constitute the first
experimental evidence for learnability differences in this domain.

Specifically, we have provided evidence that there is a universal basis for a set of primitives
organizing the person space that learners are sensitive to regardless of their native language.
Looking more closely into the nature of these primitive features, we have shown that a theory
from the particular status of the speaker feature. This sketch is very speculative, and a worked-
out implementation is beyond the scope of this article. However, this idea is in the spirit of
Harbour (2016) and Ackema and Neeleman (2018), whose theories encode an inherent asymmetry
between speaker and addressee, built into the ontology (see footnote 15). Crucially, we would
argue that this asymmetry should be treated as a bias, which shapes but does not strictly delimit
the space of possible partitions.

Before moving on, we should mention an anonymous reviewer's concerns about whether our results could be accommodated by a non-feature-based approach to person. This is a sensible worry, as it questions whether our approach truly provides evidence that the person space is represented in terms of a set of universal primitives. To address this concern, let us say a few words about whether the results reported here are compatible with putative nonfeatural representations of the person space.

Our experiments show that learners are sensitive to whether certain semantic values (e.g., speaker, addressee) are included in the pronominal reference, regardless of the specific person category. This suggests that person categories form natural classes along these semantic dimensions. Here, we have treated these natural classes as defined by primitive features. Arguably, an alternative, non-feature-based approach would be one that does not decompose person categories into smaller units, but treats them as primitives themselves; for example, first, inclusive, second, and third would be four different primitives, as well as all other plural combinations (see Cysouw 2007 for discussion). We see a problem with this type of alternative view: in order to account for our main findings, this approach would need to explain why it is that learners are more likely to collapse some person categories than others, even when these categories are nonnative.

As a response to this issue, the same reviewer conjectures that some additional pragmatic
mechanism might result in more accurate learning predictions. For the time being, however, we
remain agnostic about how this proposal could be further developed into a full theory of person
that accounts for our results (and for the typology). Instead, we maintain that, to the extent that
learners are shown to be sensitive to the semantic overlap between categories, a feature-based
account of our results is more parsimonious (as well as in line with already established theories
of person).

6 Conclusion

Person systems have been extensively explored from a theoretical standpoint: a number of ap-
proaches have been proposed, each of which constrains the set of possible person partitions that
humans can represent, with the aim of explaining the prevalence of certain partitions of the person
space crosslinguistically. The experiments reported here inform these theoretical approaches by
generating direct behavioral evidence for the impact of hypothesized representations and con-
straints on the learnability of different person partitions. Indeed, our results constitute the first
experimental evidence for learnability differences in this domain.

Specifically, we have provided evidence that there is a universal basis for a set of primitives
organizing the person space that learners are sensitive to regardless of their native language.
Looking more closely into the nature of these primitive features, we have shown that a theory
of the person space needs to account for the semantic similarity between inclusive and second persons, on the one hand, and between second and third persons, on the other. Each of these pairs of categories was treated as a natural class by learners, suggesting that they have features in common (e.g., an addressee feature possibly shared between second and inclusive persons). Besides a preference for feature-based patterns, there was evidence across our experiments that participants have an additional bias toward partitions of the person space where the speaker is distinct from other categories. Thus, even though both speakers and addressees are participants in the conversation, there is an inherent asymmetry in how learners treat them. We sketched two possible accounts of this, the first in terms of a general egocentric bias, and the second in terms of a special type of natural-class-based similarity.

More generally, our results suggest that the experimental methods developed here provide a novel tool for testing theoretically motivated questions about how languages carve up the person space. While these kinds of methods have gained traction in investigating learning biases in a number of linguistic domains, here we have highlighted the sparsity of typological data as underscoring the need for new sources of evidence in building theories of person.

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of the person space needs to account for the semantic similarity between inclusive and second persons, on the one hand, and between second and third persons, on the other. Each of these pairs of categories was treated as a natural class by learners, suggesting that they have features in common (e.g., an addressee feature possibly shared between second and inclusive persons). Besides a preference for feature-based patterns, there was evidence across our experiments that participants have an additional bias toward partitions of the person space where the speaker is distinct from other categories. Thus, even though both speakers and addressees are participants in the conversation, there is an inherent asymmetry in how learners treat them. We sketched two possible accounts of this, the first in terms of a general egocentric bias, and the second in terms of a special type of natural-class-based similarity.

More generally, our results suggest that the experimental methods developed here provide a novel tool for testing theoretically motivated questions about how languages carve up the person space. While these kinds of methods have gained traction in investigating learning biases in a number of linguistic domains, here we have highlighted the sparsity of typological data as underscoring the need for new sources of evidence in building theories of person.

## References

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Cysouw, Michael. 2007. Building semantic maps: The case of person marking. In *New challenges in typology*, ed. by Matti Miestamo and Bernhard Wälchli, 225–248. Berlin: De Gruyter Mouton.

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Martin, Alexander, and Sharon Peperkamp. 2020. Phonetically natural rules benefit from a learning bias: A re-examination of vowel harmony and disharmony. *Phonology* 37:65–90.

Martin, Alexander, Theeraporn Ratitamkul, Klaus Abels, David Adger, and Jennifer Culbertson. 2019. Cross-linguistic evidence for cognitive universals in the noun phrase. *Linguistics Vanguard* 5(1). https://doi.org/10.1515/lingvan-2018-0072.

McGinnis, Martha. 2005. On markedness asymmetries in person and number. *Language* 81:699–718.

Meier, Richard P. 1990. Person deixis in American Sign Language. *Theoretical Issues in Sign Language Research* 1:175–190.

Moreton, Elliott. 2008. Analytic bias and phonological typology. *Phonology* 25:83–127.

Moreton, Elliott, and Joe Pater. 2012. Structure and substance in artificial-phonology learning. Part I: Structure. *Language and Linguistics Compass* 6:686–701.

Moyer, Morgan, Kaitlyn Harrigan, Valentine Hacquard, and Jeffrey Lidz. 2015. 2-year-olds’ comprehension of personal pronouns. https://www.bu.edu/bucld/files/2015/06/Moyer.pdf.

Neidle, Carol, Judy Kegl, Dawn MacLaughlin, Benjamin Bahan, and Robert G. Lee. 2000. *The syntax of American Sign Language: Functional categories and hierarchical structure*. Cambridge, MA: MIT Press.
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Halle, Morris, and Alec Marantz. 1994. Some key features of Distributed Morphology. In *Papers on phonology and morphology*, ed. by Andrew Carnie and Heidi Harley, with Tony Bures, 275–288. MIT Working Papers in Linguistics 21. Cambridge, MA: MIT, MIT Working Papers in Linguistics.

Hanson, Rebecca. 2000. Pronoun acquisition and the morphological feature geometry. *Calgary Working Papers in Linguistics* 22. https://prism.ucalgary.ca/handle/1880/51442.

Hanson, Rebecca, Heidi Harley, and Elizabeth Ritter. 2000. Underspecification and universal defaults for person and number features. In *Actes du Congrès annuel de l'ACL/CLA Annual Conference Proceedings*, 111–122. Ottawa: University of Ottawa, Cahiers Linguistiques d'Ottawa.

Harbour, Daniel. 2008. On homophony and methodology in morphology. *Morphology* 18:75–92.

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Harbour, Daniel. 2014. Paucity, abundance, and the theory of number. *Language* 90:185–229.

Harbour, Daniel. 2016. *Impossible persons*. Cambridge, MA: MIT Press.

Harley, Heidi. 2008. When is a syncretism more than a syncretism? Impoverishment, metasyncretism, and underspecification. In *Phi theory: Phi-features across modules and interfaces*, ed. by Daniel Harbour, David Adger, and Susana Béjar, 251–294. Oxford: Oxford University Press.

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Kay, Paul, and Terry Regier. 2007. Color naming universals: The case of Berinmo. *Cognition* 102:289–298.

Kemp, Charles, and Terry Regier. 2012. Kinship categories across languages reflect general communicative principles. *Science* 336:1049–1054.

Ladd, D. Robert, Seán G. Roberts, and Dan Dediu. 2015. Correlational studies in typological and historical linguistics. *Annual Review of Linguistics* 1:221–241.

Loveland, Katherine A. 1984. Learning about points of view: Spatial perspective and the acquisition of ‘I/you’. *Journal of Child Language* 11:535–556.

Maldonado, Mora, and Jennifer Culbertson. 2019. Something about us: Learning first person pronoun systems. In *Proceedings of the 41st Annual Conference of the Cognitive Science Society*, ed. by Ashok Goel, Colleen Seifert, and Christian Freksa, 749–755. Montreal, QB: Cognitive Science Society.

Martí, Luisa. 2020. Inclusive plurals and the theory of number. *Linguistic Inquiry* 51:37–74.

Martin, Alexander, and Sharon Peperkamp. 2020. Phonetically natural rules benefit from a learning bias: A re-examination of vowel harmony and disharmony. *Phonology* 37:65–90.

Martin, Alexander, Theeraporn Ratitamkul, Klaus Abels, David Adger, and Jennifer Culbertson. 2019. Cross-linguistic evidence for cognitive universals in the noun phrase. *Linguistics Vanguard* 5(1). https://doi.org/10.1515/lingvan-2018-0072.

McGinnis, Martha. 2005. On markedness asymmetries in person and number. *Language* 81:699–718.

Meier, Richard P. 1990. Person deixis in American Sign Language. *Theoretical Issues in Sign Language Research* 1:175–190.

Moreton, Elliott. 2008. Analytic bias and phonological typology. *Phonology* 25:83–127.

Moreton, Elliott, and Joe Pater. 2012. Structure and substance in artificial-phonology learning. Part I: Structure. *Language and Linguistics Compass* 6:686–701.

Moyer, Morgan, Kaitlyn Harrigan, Valentine Hacquard, and Jeffrey Lidz. 2015. 2-year-olds’ comprehension of personal pronouns. https://www.bu.edu/bucld/files/2015/06/Moyer.pdf.

Neidle, Carol, Judy Kegl, Dawn MacLaughlin, Benjamin Bahan, and Robert G. Lee. 2000. *The syntax of American Sign Language: Functional categories and hierarchical structure*. Cambridge, MA: MIT Press.
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Noyer, Rolf. 1992. Features, positions and affixes in autonomous morphological structure. Doctoral dissertation, MIT.

Pagel, Mark, Quentin D. Atkinson, and Andrew Meade. 2007. Frequency of word-use predicts rates of lexical evolution throughout Indo-European history. *Nature* 449:717–720.

Perfors, Amy, Joshua B. Tenenbaum, and Terry Regier. 2011. The learnability of abstract syntactic principles. *Cognition* 118:306–338.

Pertsova, Katya. 2011. Grounding systematic syncretism in learning. *Linguistic Inquiry* 42:225–266.

Piantadosi, Steven T., and Edward Gibson. 2014. Quantitative standards for absolute linguistic universals. *Cognitive Science* 38:736–756.

Piantadosi, Steven T., Joshua B. Tenenbaum, and Noah D. Goodman. 2016. The logical primitives of thought: Empirical foundations for compositional cognitive models. *Psychological Review* 123:392–424.

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Rouse, Steven V. 2015. A reliability analysis of Mechanical Turk data. *Computers in Human Behavior* 43:304–307.

Ruffman, Ted. 2014. To belief or not belief: Children’s theory of mind. *Developmental Review* 34:265–293.

Saffran, Jenny R., and Erik D. Thiessen. 2003. Pattern induction by infant language learners. *Developmental Psychology* 39:484–494.

Saldana, Carmen, Yohei Oseki, and Jennifer Culbertson. 2019. Do cross-linguistic patterns of morpheme order reflect a cognitive bias? In *Proceedings of the 41st Annual Conference of the Cognitive Science Society*, ed. by Ashok Goel, Colleen Seifert, and Christian Freksa, 994–1000. Montreal, QB: Cognitive Science Society.

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Sonnaert, Jolijn. 2018. *The atoms of person in pronominal paradigms*. Amsterdam: Netherlands Graduate School of Linguistics (LOT).

Steinert-Threlkeld, Shane, and Jakub Szymanik. To appear. Ease of learning explains semantic universals. *Cognition*.

Tabullo, Angel, Mariana Arismendi, Alejandro Wainselboim, Gerardo Primero, Sergio Vernis, Enrique Segura, Silvano Zanutto, and Alberto Yorio. 2012. On the learnability of frequent and infrequent word orders: An artificial language learning study. *Quarterly Journal of Experimental Psychology* 65:1848–1863.

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Wechsler, Stephen. 2010. What ‘you’ and ‘I’ mean to each other: Person indexicals, self-ascription, and theory of mind. *Language* 86:332–365.

White, James. 2017. Accounting for the learnability of saltation in phonological theory: A maximum entropy model with a P-map bias. *Language* 93:1–36.
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Noyer, Rolf. 1992. Features, positions and affixes in autonomous morphological structure. Doctoral dissertation, MIT.

Pagel, Mark, Quentin D. Atkinson, and Andrew Meade. 2007. Frequency of word-use predicts rates of lexical evolution throughout Indo-European history. *Nature* 449:717–720.

Perfors, Amy, Joshua B. Tenenbaum, and Terry Regier. 2011. The learnability of abstract syntactic principles. *Cognition* 118:306–338.

Pertsova, Katya. 2011. Grounding systematic syncretism in learning. *Linguistic Inquiry* 42:225–266.

Piantadosi, Steven T., and Edward Gibson. 2014. Quantitative standards for absolute linguistic universals. *Cognitive Science* 38:736–756.

Piantadosi, Steven T., Joshua B. Tenenbaum, and Noah D. Goodman. 2016. The logical primitives of thought: Empirical foundations for compositional cognitive models. *Psychological Review* 123:392–424.

R Core Team. 2018. *R: A language and environment for statistical computing*. R Foundation for Statistical Computing, Vienna, Austria.

Rodrigues, Aryon D. 1990. You and I = Neither you nor I: The personal system of Tupinamba. In *Amazonian linguistics: Studies in lowland South American languages*, ed. by Doris L. Payne, 393–405. Austin: University of Texas Press.

Rouse, Steven V. 2015. A reliability analysis of Mechanical Turk data. *Computers in Human Behavior* 43:304–307.

Ruffman, Ted. 2014. To belief or not belief: Children’s theory of mind. *Developmental Review* 34:265–293.

Saffran, Jenny R., and Erik D. Thiessen. 2003. Pattern induction by infant language learners. *Developmental Psychology* 39:484–494.

Saldana, Carmen, Yohei Oseki, and Jennifer Culbertson. 2019. Do cross-linguistic patterns of morpheme order reflect a cognitive bias? In *Proceedings of the 41st Annual Conference of the Cognitive Science Society*, ed. by Ashok Goel, Colleen Seifert, and Christian Freksa, 994–1000. Montreal, QB: Cognitive Science Society.

Sauerland, Uli, and Jonathan David Bobaljik. 2013. Syncretism distribution modeling: Accidental homophony as a random event. In *Proceedings of GLOW in Asia IX*, ed. by Nobu Goto, Koichi Otaki, Atsushi Sato, and Kensuke Takita, 31–53. Tsu, Japan: Mie University.

Schwartz, Linda J., and Timothy Dunnigan. 1986. Pronouns and pronominal categories in Southwestern Ojibwe. In *Pronominal systems*, ed. by Ursula Wiesemann, 285–322. Tübingen: Gunter Narr Verlag.

Silverstein, Michael. 1976. Hierarchy of features and ergativity. In *Grammatical categories in Australian languages*, ed. by R. M. W. Dixon, 112–171. Canberra: Australian National University.

Sokolovskaja, Natalja K. 1980. Nekotorye semantičeskie universalii v sisteme ličnyx mestoimenij. In *Teorija i tipologija mestoimenij*, ed. by Igor F. Vardul, 84–103. Moscow: Nauka.

Sonnaert, Jolijn. 2018. *The atoms of person in pronominal paradigms*. Amsterdam: Netherlands Graduate School of Linguistics (LOT).

Steinert-Threlkeld, Shane, and Jakub Szymanik. To appear. Ease of learning explains semantic universals. *Cognition*.

Tabullo, Angel, Mariana Arismendi, Alejandro Wainselboim, Gerardo Primero, Sergio Vernis, Enrique Segura, Silvano Zanutto, and Alberto Yorio. 2012. On the learnability of frequent and infrequent word orders: An artificial language learning study. *Quarterly Journal of Experimental Psychology* 65:1848–1863.

Thomas, David. 1955. Three analyses of the Ilocano pronoun system. *Word* 11:204–208.

Wechsler, Stephen. 2010. What ‘you’ and ‘I’ mean to each other: Person indexicals, self-ascription, and theory of mind. *Language* 86:332–365.

White, James. 2017. Accounting for the learnability of saltation in phonological theory: A maximum entropy model with a P-map bias. *Language* 93:1–36.
Wilson, Colin. 2006. Learning phonology with substantive bias: An experimental and computational study of velar palatalization. *Cognitive Science* 30:945–982.

Zaslavsky, Noga, Charles Kemp, Naftali Tishby, and Terry Regier. 2019. Color naming reflects both perceptual structure and communicative need. *Topics in Cognitive Science* 11:207–219.

Zwicky, Arnold M. 1977. Hierarchies of person. In *Papers from the Thirteenth Regional Meeting, Chicago Linguistic Society*, ed. by Woodford A. Beach, Samuel E. Fox, and Shulamith Philosoph, 714–733. Chicago: University of Chicago, Chicago Linguistic Society.

Mora Maldonado
Centre for Language Evolution
University of Edinburgh
mora.maldonado@ed.ac.uk

Jennifer Culbertson
Centre for Language Evolution
University of Edinburgh
jennifer.culbertson@ed.ac.uk
Wilson, Colin. 2006. Learning phonology with substantive bias: An experimental and computational study of velar palatalization. *Cognitive Science* 30:945–982.

Zaslavsky, Noga, Charles Kemp, Naftali Tishby, and Terry Regier. 2019. Color naming reflects both perceptual structure and communicative need. *Topics in Cognitive Science* 11:207–219.

Zwicky, Arnold M. 1977. Hierarchies of person. In *Papers from the Thirteenth Regional Meeting, Chicago Linguistic Society*, ed. by Woodford A. Beach, Samuel E. Fox, and Shulamith Philosoph, 714–733. Chicago: University of Chicago, Chicago Linguistic Society.

Mora Maldonado
Centre for Language Evolution
University of Edinburgh
mora.maldonado@ed.ac.uk

Jennifer Culbertson
Centre for Language Evolution
University of Edinburgh
jennifer.culbertson@ed.ac.uk