Morphological Inflection Generation Using
Character Sequence to Sequence Learning
Manaal Faruqui1 Yulia Tsvetkov1 Graham Neubig2 Chris Dyer1
1
Language Technologies Institute, Carnegie Mellon University, USA
2
Graduate School of Information Science, Nara Institute of Science and Technology, Japan{mfaruqui,ytsvetko,cdyer}@cs.cmu.edu neubig@is.naist.jp

Abstract
Morphological inflection generation is thetask of generating the inflected form of a given
lemma corresponding to a particular linguistic transformation. We model the problem of
inflection generation as a character sequence
to sequence learning problem and present avariant of the neural encoder-decoder model
for solving it. Our model is language independent and can be trained in both supervisedand semi-supervised settings. We evaluate oursystem on seven datasets of morphologicallyrich languages and achieve either better orcomparable results to existing state-of-the-art
models of inflection generation.

1

Introduction

Inflection is the word-formation mechanism to express different grammatical categories such as tense,
mood, voice, aspect, person, gender, number andcase. Inflectional morphology is often realized by
the concatenation of bound morphemes (prefixes
and suffixes) to a root form or stem, but nonconcatenative processes such as ablaut and infixation arefound in many languages as well. Table 1 shows thepossible inflected forms of the German stem Kalb
(calf) when it is used in different cases and numbers.
The inflected forms are the result of both ablaut (e.g.,a→ä) and suffixation (e.g., +ern).
Inflection generation is useful for reducing data
sparsity in morphologically complex languages. For
example, statistical machine translation suffers fromdata sparsity when translating morphologically-richlanguages, since every surface form is considered an

nominative
accusative
dativegenitivesingular
Kalb
Kalb
Kalb
KalbespluralKälberKälberKälbernKälberTable 1: An example of an inflection table from the German
noun dataset for the word Kalb (calf).

independent entity. Translating into lemmas in thetarget language, and then applying inflection generation as a post-processing step, has been shown to
alleviate the sparsity problem (Minkov et al., 2007;
Toutanova et al., 2008; Clifton and Sarkar, 2011;
Fraser et al., 2012; Chahuneau et al., 2013a). Modeling inflection generation has also been used to improve language modeling (Chahuneau et al., 2013b),
identification of multi-word expressions (Oflazer etal., 2004), among other applications.
The traditional approach to modeling inflection relies on hand-crafted finite state transducers
and lexicography, e.g., using two-level morphology(Koskenniemi, 1983; Kaplan and Kay, 1994). Suchsystems are appealing since they correspond to linguistic theories, but they are expensive to create,
they can be fragile (Oflazer, 1996), and the composed transducers can be impractically large. Asan alternative, machine learning models have been
proposed to generate inflections from root forms
as string transduction (Yarowsky and Wicentowski,
2000; Wicentowski, 2004; Dreyer and Eisner, 2011;
Durrett and DeNero, 2013; Ahlberg et al., 2014;
Hulden, 2014; Ahlberg et al., 2015; Nicolai et al.,2015). However, these impose either assumptions
about the set of possible morphological processes

(a)

kalb
case=nominative
number=plural

inflection
generation(b) <w> x1 a(c) ax2 </w><w> x1 ä x2 er </w>ä<w> x1 a x2 es </w>aFigure 1: A general inflection generation model.
(d)2Inflection Generation: Background

Durrett and DeNero (2013) formulate the task of supervised inflection generation for a given root form,
based on a large number of training inflection tables extracted from Wiktionary. Every inflection table contains the inflected form of a given root wordcorresponding to different linguistic transformations(cf. Table 1). Figure 1 shows the inflection generation framework. Since the release of the Wiktionary
dataset, several different models have reported performance on this dataset. As we are also using thisdataset, we will now review these models.
We denote the models of Durrett and DeNero1

www.wiktionary.org

a l b </w>
ä l b e r </w>
<w> k a l b e s </w><w> kkälber(e.g. affixation) or require careful feature engineering.
In this paper, we present a model of inflection
generation based on a neural network sequence tosequence transducer. The root form is represented
as sequence of characters, and this is the input toan encoder-decoder architecture (Cho et al., 2014;
Sutskever et al., 2014). The model transforms its input to a sequence of output characters representing
the inflected form (§4). Our model makes no assumptions about morphological processes, and our
features are simply the individual characters. The
model is trained on pairs of root form and inflected
forms obtained from inflection tables extracted from
Wiktionary.1 We improve the supervised model with
unlabeled data, by integrating a character language
model trained on the vocabulary of the language.
Our experiments show that the model achieves
better or comparable results to state-of-the-art methods on the benchmark inflection generation tasks(§5). For example, our model is able to learn longrange relations between character sequences in thestring aiding the inflection generation process required by Finnish vowel harmony (§6), which helps
it obtain the current best results in that language.

<w> k

a
ä

a
a

k
er </w> es </w> k

</w>

</w>

</w>

er </w>
es </w>llbb

Figure 2: Rule extraction: (a) Character aligned-table; (b)Table-level rule of AFH14, AFH15 (c) Vertical rules of DDN13and (d) Atomic rules of NCK15.

(2013), Ahlberg et al. (2014), Ahlberg et al. (2015),
and Nicolai et al. (2015), by DDN13, AFH14,
AFH15, and NCK15 respectively. These models
perform inflection generation as string transduction
and largely consist of three major components: (1)Character alignment of word forms in a table; (2)Extraction of string transformation rules; (3) Application of rules to new root forms.
The first step is learning character alignments
across inflected forms in a table. Figure 2 (a) showsalignment between three word forms of Kalb. Different models use different heuristic algorithms foralignments such as edit distance, dynamic edit distance (Eisner, 2002; Oncina and Sebban, 2006),
and longest subsequence alignment (Bergroth et al.,2000). Aligning characters across word forms provide spans of characters that have changed and spansthat remain unchanged. These spans are used to extract rules for inflection generation for different inflection types as shown in Figure 2 (b)–(d).
By applying the extracted rules to new root forms,
inflected words can be generated. DDN13 use asemi-Markov model (Sarawagi and Cohen, 2004) topredict what rules should be applied, using character n-grams (n = 1 to 4) as features. AFH14 andAFH15 use substring features extracted from words
to match an input word to a rule table. NCK15 use
a semi-Markov model inspired by DDN13, but additionally use target n-grams and joint n-grams asfeatures sequences while selecting the rules.
Motivation for our model. Morphology often
makes references to segmental features, like placeor manner of articulation, or voicing status (Chom-sky and Halle, 1968). While these can be encoded
as features in existing work, our approach treats segments as vectors of features “natively”. Our approach represents every character as a bundle of continuous features, instead of using discrete surface
character sequence features. Also, our model uses
features as part of the transduction rules themselves,
whereas in existing work features are only used torescore rule applications.
In existing work, the learner implicitly specifies the class of rules that can be learned, suchas “delete” or “concatenate”. To deal with phenomenona like segment lengthening in English: run→ running; or reduplication in Hebrew: Kelev →Klavlav, Chatul → Chataltul; (or consonant gradation in Finnish), where the affixes are induced fromcharacters of the root form, one must engineer a newrule class, which leads to poorer estimates due todata sparsity. By modeling inflection generation asa task of generating a character sequence, one character at a time, we do away with such problems.

encoded input vector e and all the previously predicted outputs hy1 , · · · yt−1 i. In other words, the decoder defines a probability over the output sequence~y = hy1 , · · · , yT 0 i by decomposing the joint probability into ordered conditionals:p(~y |~x) =

YT 0
t=1

p(yt |e, hy1 , · · · , yt−1 i)(2)With a decoder RNN, we can first obtain the hidden
layer at time t as: st = g(st−1 , {e, yt−1 }) and feed
this into a softmax layer to obtain the conditional
probability as:p(yt = i|e, ~y<t ) = softmax(Ws st + bs )i(3)

where, ~y<t = hy1 , · · · , yt−1 i. In recent work, bothf and g are generally LSTMs, a kind of RNN which
we describe next.
3.2

Long Short-Term Memory (LSTM)

Here, we describe briefly the underlying frameworkof our inflection generation model, called the recurrent neural network (RNN) encoder-decoder (Cho etal., 2014; Sutskever et al., 2014) which is used totransform an input sequence ~x to output sequence ~y .
We represent an item by x, a sequence of items by~x, vectors by x, matrices by X, and sequences ofvectors by ~x.

In principle, RNNs allow retaining information fromtime steps in the distant past, but the nonlinear“squashing” functions applied in the calculation ofeach ht result in a decay of the error signal used intraining with backpropagation. LSTMs are a variant of RNNs designed to cope with this “vanishing gradient” problem using an extra memory “cell”(Hochreiter and Schmidhuber, 1997; Graves, 2013).
Past work explains the computation within an LSTM
through the metaphors of deciding how much of thecurrent input to pass into memory or forget. We referinterested readers to the original papers for details.

3.1

4

3

Neural Encoder-Decoder Models

Formulation

In the encoder-decoder framework, an encoder reads
a variable length input sequence, a sequence of vectors ~x = hx1 , · · · , xT i (corresponding to a sequenceof input symbols ~x = hx1 , · · · , xT i) and generates
a fixed-dimensional vector representation of the sequence. xt ∈ Rl is an input vector of length l. The
most common approach is to use an RNN such that:ht = f (ht−1 , xt )(1)

where ht ∈ Rn is a hidden state at time t, and f
is generally a non-linear transformation, producing
e := hT +1 as the input representation. The decoderis trained to predict the next output yt given theInflection Generation ModelWe frame the problem of inflection generation as asequence to sequence learning problem of character sequences. The standard encoder-decoder models were designed for machine translation where
the objective is to translate a sentence (sequence ofwords) from one language to a semantically equivalent sentence (sequence of words) in another language. We can easily port the encoder-decodertranslation model for inflection generation. Ourmodel predicts the sequence of characters in the inflected string given the characters in the root word
(input).
However, our problem differs from the above setting in two ways: (1) the input and output character

e
k

<w>
<w>

k

a

l

k
e

b </w>

ä

k
a
e

l

ä
l
e

b

l
b
e

e

b

r

e
ε
e

ε
e

</w>

r
ε
e

Figure 3: The modified encoder-decoder architecture for inflection generation. Input characters are shown in black and predictedcharacters are shown in red.

· indicates the append operation.

sequences are mostly similar except for the inflections; (2) the input and output character sequences
have different semantics. Regarding the first difference, taking the word play as an example, the inflected forms corresponding to past tense and continuous forms are played and playing. To better use
this correspondence between the input and output
sequence, we also feed the input sequence directly
into the decoder:

4.1

Supervised Learning

The parameters of our model are the set ofcharacter vectors, the transformation parameters(Wtrans , btrans ), and the parameters of the encoderand decoder LSTMs (§3.2). We use negative loglikelihood of the output character sequence as theloss function:
XT 0−log p(~y |~x) = −log p(yt |e, ~y<t )(6)t=1

st = g(st−1 , {e, yt−1 , xt })(4)

where, g is the decoder LSTM, and xt and yt are theinput and output character vectors respectively. Because the lengths of the input and output sequences
are not equal, we feed an  character in the decoder,indicating null input, once the input sequence runsout of characters. These  character vectors are parameters that are learned by our model, exactly asother character vectors.
Regarding the second difference, to provide themodel the ability to learn the transformation of semantics from input to output, we apply an affine
transformation on the encoded vector e:e ← Wtrans e + btrans(5)where, Wtrans , btrans are the transformation parameters. Also, in the encoder we use a bidirectional LSTM (Graves et al., 2005) instead ofa uni-directional LSTM, as it has been shown tocapture the sequence information more effectively(Ling et al., 2015; Ballesteros et al., 2015; Bahdanau et al., 2015). Our resultant inflection generation model is shown in Figure 3.

We minimize the loss using stochastic updates with
AdaDelta (Zeiler, 2012). This is our purely supervised model for inflection generation and we evaluate it in two different settings as established by previous work:
Factored Model. In the first setting, we learn aseparate model for each type of inflection independent of the other possible inflections. For example,
in case of German nouns, we learn 8, and for German verbs, we learn 27 individual encoder-decoder
inflection models (cf. Table 3). There is no parameter sharing across these models. We call these factored models of inflection generation.
Joint Model. In the second setting, while learning a model for an inflection type, we also use theinformation of how the lemma inflects across allother inflection types i.e., the inflection table of aroot form is used to learn different inflection models. We model this, by having the same encoder
in the encoder-decoder model across all inflection
models.2 The encoder in our model is learning a2

We also tried having the same encoder and decoder acrossinflection types, with just the transformation matrix being dif-pLM (~y )len(~y ) - len(~x)
same-suffix(~y , ~x)?
same-prefix(~y , ~x)?

p(~y |~x)
levenshtein(~y , ~x)subsequence(~y , ~x)?
subsequence(~x, ~y )?

DatasetGerman Nouns (DE-N)
German Verbs (DE-V)
Spanish Verbs (ES-V)
Finnish NN & Adj. (FI-NA)
Finnish Verbs (FI-V)
Dutch Verbs (NL-V)
French Verbs (FR-V)

Table 2: Features used to rerank the inflected outputs. ~x, ~ydenote the root and inflected character sequences resp.

representation of the input character sequence. Because all inflection models take the same input but
produce different outputs, we hypothesize that having the same encoder can lead to better estimates.
4.2

Semi-supervised Learning

The model we described so far relies entirely on theavailability of pairs of root form and inflected wordform for learning to generate inflections. Althoughsuch supervised models can be used to obtain inflection generation models (Durrett and DeNero, 2013;
Ahlberg et al., 2015), it has been shown that unlabeled data can generally improve the performanceof such systems (Ahlberg et al., 2014; Nicolai et al.,2015). The vocabulary of the words of a language
encode information about what correct sequences ofcharacters in a language look like. Thus, we learn
a language model over the character sequences ina vocabulary extracted from a large unlabeled corpus. We use this language model to make predictions about the next character in the sequence given
the previous characters, in following two settings.
Output Reranking. In the first setting, we firsttrain the inflection generation model using the supervised setting as described in §4.1. While making predictions for inflections, we use beam searchto generate possible output character sequences andrerank them using the language model probability
along with other easily extractable features as described in Table 2. We use pairwise ranking optimization (PRO) to learn the reranking model (Hopkins and May, 2011). The reranker is trained on the
beam output of dev set and evaluated on test set.
Language Model Interpolation. In the second
setting, we interpolate the probability of observing
the next character according to the language modelwith the probability according to our inflection genferent (equ. 5), and observed consistently worse results.

root forms
2764
2027
4055
6400
7249
11200
6957

Infl.
8
27
57
28
53
9
48

Table 3: The number of root forms and types of inflections
across datasets.

eration model. Thus, the loss function becomes:
1 XT 0−log p(~y |~x) =− log p(yt |e, ~y<t )t=1
Z− λlog pLM (yt |~y<t ) (7)where pLM (yt |~y<t ) is the probability of observing
the word yt given the history estimated according toa language model, λ ≥ 0 is the interpolation parameter which is learned during training and Z is
the normalization factor. This formulation lets us
use any off-the-shelf pre-trained character language
model easily (details in §5).
4.3

Ensembling

Our loss functions (equ. 6 & 7) formulated using aneural network architecture are non-convex in nature
and are thus difficult to optimize. It has been shownthat taking an ensemble of models which were initialized differently and trained independently leads
to improved performance (Hansen and Salamon,
1990; Collobert et al., 2011). Thus, for each modeltype used in this work, we report results obtainedusing an ensemble of models. So, while decoding
we compute the probability of emitting a character as the product-of-experts of the individual modQ
1
els in the ensemble: pens (yt |·) = Z1 ki=1 pi (yt |·) k
where, pi (yt |·) is the probability according to i-thmodel and Z is the normalization factor.

5

Experiments

We now conduct experiments using the describedmodels. Note that not all previously published models present results on all settings, and thus we compare our results to them wherever appropriate.
Hyperparameters. Across all models describedin this paper, we use the following hyperparameters.

In both the encoder and decoder models we use single layer LSTMs with the hidden vector of length
100. The length of character vectors is the size ofcharacter vocabulary according to each dataset. The
parameters are regularized with `2 , with the regularization constant 10−5 .3 The number of models for
ensembling are k = 5. Models are trained for at
most 30 epochs and the model with best result on
development set is selected.

DE-V
DE-N
ES-V
FI-V
FI-NA
NL-V
FR-V
Avg.

DDN13
94.76
88.31
99.61
97.23
92.14
90.50
98.80
94.47

NCK15
97.50
88.60
99.80
98.10
93.00
96.10
99.20
96.04

Ours
96.72
88.12
99.81
97.81
95.44
96.71
98.82
96.20

Table 4: Individual form prediction accuracy for factored su-

5.1

Data

Durrett and DeNero (2013) published the Wiktionary inflection dataset with training, development
and test splits. The development and test sets contain 200 inflection tables each and the training setsconsist of the remaining data. This dataset contains inflections for German, Finnish and Spanish. This dataset was further augmented by (Nicolai et al., 2015), by adding Dutch verbs extracted
from CELEX lexical database (Baayen et al., 1995),
French verbs from Verbsite, an online French conjugation dictionary and Czech nouns and verbs
from the Prague Dependnecy Treebank (Hajič et al.,2001). As the dataset for Czech contains many incomplete tables, we do not use it for our experiments. These datasets come with pre-specified training/dev/test splits, which we use. For each of these
sets, the training data is restricted to 80% of the total inflection tables, with 10% for development and
10% for testing. We list the size of these datasets inTable 3.
For semi-supervised experiments, we train a 5gram character language model with Witten-Bellsmoothing (Bell et al., 1990) using the SRILM
toolkit (Stolcke, 2002). We train the character language models on the list of unique word types extracted from the Wikipedia dump for each language
after filtering out words with characters unseen in
the inflection generation training dataset. We obtained around 2 million unique words for each language.
5.2

Results

Supervised Models. The individual inflected
form accuracy for the factored model (§4.1) is shownin Table 4. Across datasets, we obtain either com3

Using dropout did not improve our results.

pervised models.

DE-V
DE-N
ES-V
FI-V
FI-NA
Avg.
NL-V
FR-V
Avg.

DDN13
96.19
88.94
99.67
96.43
93.41
94.93
93.88
98.60
95.30

AFH14
97.01
87.81
99.52
96.36
91.91
94.53
–
–
–

AFH15
98.11
89.88
99.92
97.14
93.68
95.74
–
–
–

Ours
97.25
88.37
99.86
97.97
94.71
95.63
96.16
98.74
96.15

Table 5: Individual form prediction accuracy for joint supervised models.

parable or better results than NCK15 while obtaining on average an accuracy of 96.20% which ishigher than both DDN13 and NCK15. Our factoredmodel performs better than DDN13 and NCK15
on datasets with large training set (ES-V, FI-V, FINA, NL-V, FR-V) as opposed to datasets with small
training set (DE-N, DE-V). In the joint model setting (cf. Table 5), on average, we perform better
than DDN13 and AFH14 but are behind AFH15
by 0.11%. Our model improves in performanceover our factored model for DE-N, DE-V, and ES-V,
which are the three smallest training datasets. Thus,
parameter sharing across different inflection types
helps the low-resourced scenarios.4
Semi-supervised Models. We now evaluate theutility of character language models in inflection
generation, in two different settings as described earlier (§4.2). We use the factored model as our basemodel in the following experiments as it performed
4

Although NCK15 provide results in the joint model setting,they also use raw data in the joint model which makes it incomparable to our model and other previous models.

NCK15
97.90
89.90
99.90
98.10
93.60
95.88
96.60
99.20
96.45

Interpol
96.79
88.31
99.78
96.66
94.60
95.42
96.66
98.81
96.08

100

Rerank
97.11
89.31
99.94
97.62
95.66
95.93
96.64
98.94
96.45

98
Accuracy (%)

DE-V
DE-N
ES-V
FI-V
FI-NA
Avg.
NL-V
FR-V
Avg.

AFH14
97.87
91.81
99.58
96.63
93.82
95.93
–
–
–

90

semi-supervised models.

Accuracy
79.08
95.64
84.04
96.20

Table 7: Avg. accuracy across datasets of the encoder-decoder,attentional encoder-decoder & our model without encoder.

better than the joint model (cf. Table 4 & 5). Ourreranking model which uses the character language
model along with other features (cf. Table 2) to select the best answer from a beam of predictions, improves over almost all the datasets with respect to thesupervised model and is equal on average to AFH14
and NCK15 semi-supervised models with 96.45%
accuracy. We obtain the best reported results on
ES-V and FI-NA datasets (99.94% and 95.66% respectively). However, our second semi-supervised
model, the interpolation model, on average obtains
96.08% and is surprisingly worse than our supervised model (96.20%).
Comparison to Other Architectures. Finally it
is of interest how our proposed model compares tomore traditional neural models. We compare ourmodel against a standard encoder-decoder model,
and an encoder-decoder model with attention, bothtrained on root form to inflected form character
sequences. In a standard encoder-decoder model(Sutskever et al., 2014), the encoded input sequence
vector is fed into the hidden layer of the decoder as
input, and is not available at every time step in contrast to our model, where we additionally feed in xt
at every time step as in equ. 4. An attentional modelcomputes a weighted average of the hidden layer of

94

Ours
DDN13
NCK15

92

Table 6: Individual form prediction accuracy for factored

Model
Encoder-Decoder
Encoder-Decoder Attention
Ours W/O Encoder
Ours

96

5

10
15
Word length

20

Figure 4: Plot of inflection prediction accuracy against thelength of gold inflected forms. The points are shown with minor
offset along the x-axis to enhance clarity.

the input sequence, which is then used along withthe decoder hidden layer to make a prediction (Bahdanau et al., 2015). These models also do not takethe root form character sequence as inputs to the decoder. We also evaluate the utility of having an encoder which computes a representation of the input
character sequence in a vector e by removing the encoder from our model in Figure 3. The results in Table 7 show that we outperform the encoder-decoder
model, and the model without an encoder substantially. Our model is slightly better than the attentional encoder-decoder model, and is simpler as it
does not have the additional attention layer.

6

Analysis

Length of Inflected Forms. In Figure 4 we show
how the prediction accuracy of an inflected form
varies with respect to the length of the correct inflected form.To get stable estimates, we bin the inflected forms according to their length: < 5, [5, 10),
[10, 15), and ≥ 15. The accuracy for each bin ismacro-averaged across 6 datasets5 for our factoredmodel and the best models of DDN13 and NCK15.
Our model consistently shows improvement in performance as word length increases and is significantly better than DDN13 on words of length morethan 20 and is approximately equal to NCK15. On
words of length < 5, we perform worse than DDN13
5

We remove DE-N as its the smallest and shows high variance in results.

but better than NCK15. On average, our model has
the least error margin across bins of different word
length as compared to both DDN13 and NCK15.
Using LSTMs in our model helps us make better
predictions for long sequences, since they have theability to capture long-range dependencies.
Finnish Vowel Harmony. Our model obtains thecurrent best result on the Finnish noun and adjective
dataset, this dataset has the longest inflected words,
some of which are > 30 characters long. Finnish exhibits vowel harmony, i.e, the occurrence of a vowel
is controlled by other vowels in the word. Finnish
vowels are divided into three groups: front (ä, ö,y), back (a, o, u), and neutral (e, i). If back vowels are present in a stem, then the harmony is back(i.e, front vowels will be absent), else the harmony isfront (i.e, back vowels will be absent). In compoundwords the suffix harmony is determined by the final
stem in the compound. For example, our model correctly inflects the word fasisti (fascist) to obtain fasisteissa and the compound tärkkelyspitoinen (starchcontaining) to tärkkelyspitoisissa. The ability of ourmodel to learn such relations between these vowels
helps capture vowel harmony. For FI-NA, our modelobtains 99.87% for correctly predicting vowel harmony, and NCK15 obtains 98.50%.We plot the character vectors of these Finnish vowels (cf. Figure 5)
using t-SNE projection (van der Maaten and Hinton, 2008) and observe that the vowels are correctly
grouped with visible transition from the back to thefront vowels.

7

Related Work

Similar to the encoder in our framework, Rastogi etal. (2016) extract sub-word features using a forwardbackward LSTM from a word, and use them in a traditional weighted FST to generate inflected forms.
Neural encoder-decoder models of string transduction have also been used for sub-word level transformations like grapheme-to-phoneme conversion (Yaoand Zweig, 2015; Rao et al., 2015).
Generation of inflectional morphology has been
particularly useful in statistical machine translation, both in translation from morphologically richlanguages (Goldwater and McClosky, 2005), andinto morphologically rich languages (Minkov et al.,2007; Toutanova et al., 2008; Clifton and Sarkar,

Figure 5: Plot of character vectors of Finnish vowels. Theirorganization shows that front, back and neutral vowel groups
have been discovered. The arrows show back and front vowel
correspondences.

2011; Fraser et al., 2012). Modeling the morphological structure of a word has also shown to improve
the quality of word clusters (Clark, 2003) and word
vector representations (Cotterell and Schütze, 2015).
Inflection generation is complementary to the taskof morphological and phonological segmentation,
where the existing word form needs to be segmented
to obtained meaningful sub-word units (Creutz andLagus, 2005; Snyder and Barzilay, 2008; Poon etal., 2009; Narasimhan et al., 2015; Cotterell et al.,2015; Cotterell et al., 2016). An additional line ofwork that benefits from implicit modeling of morphology is neural character-based natural language
processing, e.g., part-of-speech tagging (Santos andZadrozny, 2014; Ling et al., 2015) and dependency
parsing (Ballesteros et al., 2015). These models
have been successful when applied to morphologically rich languages, as they are able to capture word
formation patterns.

8Conclusion

We have presented a model that generates inflected
forms of a given root form using a neural network
sequence to sequence string transducer. Our modelobtains state-of-the-art results and performs at par or
better than existing inflection generation models onseven different datasets. Our model is able to learn
long-range dependencies within character sequences
for inflection generation which makes it speciallysuitable for morphologically rich languages.

Acknowledgements
We thank Mans Hulden for help in explaining
Finnish vowel harmony, and Garrett Nicolai formaking the output of his system available for comparison. This work was sponsored in part by the
National Science Foundation through award IIS1526745.

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