First–and only first because I want to leave the mea culpas for the end–I meant inconvenient to the speaker, not to the listener (who is really secondary to this discussion). And convenience isn’t simply a matter of convention: I can speak and brush my hair, say, at the same time, which somebody who has to sign with their hands can’t do. That’s all I meant.
Second, I don’t dispute that speakers of English, say, can sometimes “think in English”, where “think in English” is shorthand for “use some of the conventions of the language as a shortcut tool for thinking” (more about this in the “what I got wrong” section below). I’ve seen musicians talk to each other “in music”, so I can easily believe they’re capable of “thinking” in music. In my own experience, as I get more familiar with programming, it is sometimes easier to just “think in C++” instead of trying to translate some idea into C++. But, if this isn’t exclusively the only way to think (see below about the “if”), we still have to ask what happens when this isn’t the way the thinking happened. Answer: mentalese.
Now, on to what I got wrong:
a) I said “different versions” of sign language, instead of different sign languages. (Having never used a signed language,) I got this wrong.
b) My thoughts on whether language can affect thought have changed after I read Guy Deutscher‘s incredibly good books on language: both The Unfolding of Language and Through the Language Glass are masterpieces of persuasive writing and I highly recommend them. My favourite example from Through the… is where Deutscher talks of a tribe in Australia whose language, Guugu Yimithirr, only contains the cardinal directions (North, South, East, West). Native speakers of this language, it seems, are able to keep track of which way is North far better than speakers of a language that also uses user-fixed directions – left, right, forwards, backwards(*footnote1).
This is not at all to say that speakers of this language don’t–much less can’t–understand what ‘left’ or ‘right’ are. They just have a point on the rest of us when it comes to keeping track of which way is North.
This is also not proof that the speakers of Guugu Yimithirr “think in” Guugu Yimithirr. The speaker of the language is forced to keep track of the cardinal directions in order to be able to talk coherently. If people “thought in” a certain language–if we could only “think in” a certain language–then we would be arguing that speakers of a language such as Guugu Yimithirr don’t understand the concepts of ‘left’ and ‘right’.
My point is this: “thinking in a language” is a convenient shorthand for letting the structure of the language guide your thinking; but we’re setting ourselves up for a lot of confusion if we take the idea literally.
1) “Native” speakers are people who were raised from infancy speaking the language. Also, there’s a proper word for “user-fixed” directions