> Yeah, personally - and this might be a controversial opinion - I think most people who say they have an inner monologue are actually misattributing either their experience of reading text, or of planning hypothetical conversations with other people.

No, we aren't. Now its true that (well, for me at least) the inner monologue is the exact same experience as when reading text or when planning hypothetical conversations. Or when thinking ahead of words to write. The difference is that it is not planning a hypothetical conversation or something to write, and there is no text being read, and it happens pretty much all the time, except when I'm doing one of those other things (and sometimes as an intrusive interruptions when I am.) If you imagine there exists a common piece of mental infrastructure that is used for each of those actions, its as if it was always on doing a narration except when you are specifically, actively concentrating on using it for some other purpose.

> Hearing voices is schizophrenia.

No, hearing voices that aren't there is an auditory hallucination. Among the things it can be a symptom of is schizophrenia, but "X can be a symptom of Y" is not the same thing as "X is Y".

But an inner monologue is not an auditory hallucination. Its obviously and distinctly internal, not something that "sounds" like it is coming from outside.

> You might classify talking to yourself as a monologue

Because it literally is.

> but when most people discuss this topic, it sounds like they're describing a dialogue (i.e. one between multiple people). That seems crazy to me, because who does the other voice belong to?

I think a lot of people do what amounts to roleplaying out conversations, particular on decisions which are troublesome, with themselves; because this is similar to planning a hypothetic conversation with another person, which I gather people without inner monologues can do without outward speech, I'm not sure how connected it is to an inner monologue. From the perspective of someone with one, its a fairly easy deliberate "mode switch" where you basically decided that that is what the monologue is going to focus on.

It's also conceivable that, within plural systems, there is what amounts to an "inner dialogue" or "inner multiparty conversation". Not being a plural system, I can't comment on that and the degree to which it is perceptually different than an inner monologue.

> If you have an inner monologue, then by definition you should be able to predict what it's going to say - because mono- means just you.

That...doesn't follow. But if you have an experience of a conscious thought of what you are about just instantaneously before you say it, an inner monologue is a lot like that, but without the follow-through of speech. That is, I think you are not only wrong that it is true "by definition" that you should be able to predict an inner monologue, and that this is a false analogy to external speech, but that an inner monologue is perceptually similar to, and may well be fundamentally resusing the same infrastructure as, the natural internal "prediction" (or planning; not sure those things are, in this case, different) of outward-directed speech.