Consciousness and Language
If the mind is computational, then there must be a language of thought. This is because computations are operations defined over symbols: thought processes must be symbolic processes. The original conception of a Turing machine makes this very clear, since the operation of writing and erasing marks on a tape is obviously a process defined over symbols (ones and zeros, or numerals thereof). But the generalized notion of a computation, which involves any procedure of symbolic manipulation, will also entail that there is a language of thought, granted that thought processes are (or involve) computational processes. Thoughts will consist of, or be encoded in, sequences of word-like elements upon which operations are performed by something like a computer program. We have good reasons to believe that the mind is computational (which I won’t rehearse), so we have good reasons to believe in a language of thought. Moreover, the hypothesis of a language of thought helps deal with various conceptual and empirical problems.
And yet there is a marked reluctance to accept it. Why? I think the main reason for this reluctance is that we do not perceive the language of thought (call it LT). We do not see or hear the words that compose it; neither do we introspect these words. By contrast, we do see and hear (and sometimes introspect) the words of our ordinary public language (call this LC for “language of communication”).  That is, we are conscious of LC but we are notconscious of LT. I am now looking at words of my LC as I write, but as I think I am not in any analogous cognitive relation to the words of my LT. The language of thought is an unconscious language—not repressed, to be sure, but deeply hidden, inaccessible to consciousness. Why LT should be hidden is an interesting question, with no obvious answer, but it evidently is (granted its existence). It exists in the mind, entering into mental computations, but it does not exist in consciousness. It affects the conscious mind, leading us to form conscious thoughts we couldn’t have without it, but it never reveals itself to consciousness—it hovers in the background, invisibly and inaudibly. Thus we have no direct knowledge of its existence; its existence is inferred. We do not believe in a language of thought because of the manifest contents of consciousness, as we believe in thoughts, emotions, and sensations; we believe in it in the way we believe in atoms or genes. In fact, no one has ever caught a glimpse of LT and it remains elusive—we don’t even know what its lexicon looks like. It must contain symbols with an arbitrary connection to what they denote and with their own internal composition, but we don’t know what these symbols are—we don’t know the alphabet out of which the lexicon of LT is constructed. This epistemological situation is surely a large part of the reason that people doubt that a language of thought exists—no one has ever seen or heard the words that compose it. By contrast, we have no trouble accepting that LC exists, because we have all seen the words of LC: we are conscious of the words of LC in multiple ways—by seeing them written down, hearing them spoken, producing them in speech, and introspecting them in inner speech. It is not that we have merely theoretical reasons to believe in LC; we have direct evidence that LC exists. Because of this epistemic asymmetry we are apt to be skeptical of LTand accepting of LC.
Now it is not that this asymmetry constitutes a good reason to believe in LC but not in LT, on pain of doubting every theoretical entity we have ever had reason to posit; and there is ample precedent for the notion of unconscious mental realities. But as a matter of human psychology people have a tendency to believe in what they can sense and to doubt what they cannot. To be conscious of something is always the strongest reason for believing in it. The point I want to make is that the epistemic asymmetry is entirely contingent and should not be interpreted as having ontological significance; it is merely epistemological. I aim to loosen the hold of the conviction that LT is suspect while LC is pucker. I shall do this by inverting the epistemology of the two languages: in a conceivable case we could be conscious of the language of thought but not conscious of the language of communication. And just as in such a case we should not interpret the epistemic asymmetry as having ontological significance, so we should not do so as things actually are with us. It merely happens that we have direct evidence of LC and not of LT; there is nothing metaphysically deep here. It might have been otherwise. It is not of the essence of LT to be unconscious and of the essence of LC to be conscious; the epistemic asymmetry is not built into their very nature.
Consider then the following imaginary case. First we suppose that LT is conscious for certain possible thinkers; for concreteness suppose that LT is Latin (once the language of learned European thought). Whenever these possible thinkers think, sentences of Latin surge conspicuously through their consciousness, encoding their thoughts. They have inherited this language from their ancestors and it is built into their genes (don’t ask me how). Mental computations are performed on Latin strings and the resulting thoughts contain words of Latin. Maybe these strings enter consciousness in some sensory mode—auditory images perhaps, or possibly visual. Just as we can introspect our conscious inner speech in our acquired language, so they can introspect their innate language of thought. This seems perfectly possible. It will then not be a difficult task to persuade them that they have a language of thought: that is evident from their everyday consciousness and everyone agrees about what this language is like. It is quite evident to them that they think in Latin; they have direct knowledge of this fact. There are no debates about whether such a language exists or what composes it; it is as clear as conscious thought itself. They can in good conscience avail themselves of the theoretical benefits of positing an LT—except that they don’t posit it, since they are acquainted with it. It might be that their spoken language is derived from their internal language—they speak Latin because they think Latin. They have molded their LC around their LT, quite deliberately; or perhaps evolution has taken a short cut to producing a communicative language by simply co-opting the language already coded in their genes. Given their epistemic relation to their language of thought, there will not be much controversy about invoking it in theoretical contexts.
But what about LC and consciousness—how could its existence be a matter of conjecture, inference, and speculative positing? Aren’t our possible people bound to know it directly? Perhaps surprisingly, the answer is no. LC could be inaccessible to consciousness, just as LT is for us. For consider speakers with a kind of linguistic blindsight: when sentences are uttered in their presence they have no conscious impression of sound—it is as if they are deaf—but still the auditory input is processed by the brain, producing a belief about what was communicated. They know that the speaker said that p by producing certain sounds, but they have no consciousness of those sounds—they are processed unconsciously. Thus they have no consciousness of the words that compose their LC: all the work of hearing, parsing, and comprehension is done behind the scenes, with only the output reaching conscious awareness. We can suppose that no one has ever had a conscious percept of the words of their LC, their sound or shape, while they have all had conscious awareness of their LT. What they have in respect of LC is deafhearing: they hear (process) the words unconsciously, but they are deaf to them consciously. What they hear in this mode is inaccessible to consciousness. It is just like regular blindsight with respect to written words: someone might direct their eyes at written language and have no conscious impression of what is before them, yet the visual system might be able to process the stimuli in such a way as to produce knowledge of the inscription in question. They might engage in “blind-reading” through their eyes. Such a person could not tell you what the words they see (process) look like, since they are never conscious of these words, but the words exist and the person responds to them. Similarly, they might be able to produce spoken strings and yet not be conscious of their actions: it is all done behind the scenes with no awareness of what sounds are being produced. We are not normally conscious of the fine structure of our actions and many animals presumably lack consciousness of their motor activity (consider insects); well, these speakers lack any conscious knowledge of their speech acts—though they perform them perfectly adequately. In sum, they are not acquainted with their LC: it exists and they use it, but they are not conscious of its intrinsic character—its alphabet, phonetic properties, intonation patterns, etc. It is, as far as they are concerned, an unconscious language. We might compare it to the communication system used by bees: I don’t know whether bees are conscious (I rather think they are) but we can suppose that they are not, and then their language is an unconscious language—no bee is conscious of the words that compose its language. That doesn’t prevent bee language from existing. Bees just happen not have any conscious awareness of the language they employ. There is no necessity for a public language of communication to be conscious. 
Given this description of my hypothetical language users, what is their theoretical position vis-à-vis LT and LC? They invert our ontological prejudices. They have no scruples about believing in a language of thought, but they have their doubts about a language of communication. They may allow that an LC must exist, given that they communicate and understand each other, but the lack of direct evidence troubles them, and some may be openly skeptical. Some may make a living out of denying that there is a language of communication at all. After all, no one has ever directly observed LC, and the idea of an unconscious language strikes some as inherently problematic. They have no trouble with LT, however, since it is so evident to consciousness—as certain as thought itself (“I think in Latin” is indubitable for them). They don’t feel the need to prove the existence of LT, but they do think that the hypothesis of LC cries out for some sort of defense—perhaps arguing that it is entailed by a computational view of communication. But we can see from the outside that they are overly impressed by their own epistemological biases, reading far too much into them. We know that their LC exists, even if they doubt it. Just because they are not consciously aware of the words of LC doesn’t mean that there are none or that there is anything metaphorical or suspect about the notion of a language of communication. This is just a contingent fact about their epistemic powers. Similarly, it is just a contingent fact about our epistemic powers that we are conscious of our public language but not of our private language. There is a hidden language of thought—there has to be if the mind is computational—but we don’t happen to be conscious of it. Maybe we are indirectly conscious of it, because we are conscious of the work it does, but we are not conscious of it in its entirety. In the same way, my inverted speakers may have glimmerings of the public language they use because of their awareness of its effects in their consciousness, but they are (by hypothesis) not aware of the full nature of LC. We would think them irrational, or excessively cautious, if they were seriously to doubt the existence of a language of communication; but then why are we being commendably skeptical about the existence of a language of thought? If we have solid arguments that there must be an LT, why should its inaccessibility to consciousness count against its existence? Why should a language we use necessarily be a language of which we are conscious? Perhaps there are good biological reasons that we are not conscious of our LT (it would clutter up our attention or be too costly metabolically), but these are not reasons to doubt its existence. After all, we are not conscious of a lot of what goes in with our ordinary spoken language too. In the case of bees it may well be that their communicative language has an internal counterpart that helps them navigate the world—a language of bee thought—and it too will be an unconscious language. Bees may have both an LC and an LT with neither of them conscious, simply because bees are not conscious–or whatever smidgen of consciousness they possess is not directed at their linguistic skills.
I end with this thought: perhaps the reason we are not conscious of the language of thought is that it is just too abstract to enter our consciousness. The symbols in LT are universal to the human species, so they are less specific than the symbols of a spoken language (or a sign language). They are components of an abstract computational structure. Just as we cannot have in mind an image of a triangle in general, but only specific types of triangle, so we cannot have in mind a word belonging to an abstract universal language, but only words belonging to a particularized language. Consciousness will not admit elements of the requisite generality and abstractness: for how could such elements be contents of consciousness? We can have concepts of abstract things, but it is harder to see how the conscious linguistic medium of concepts could itself be abstract. Consciousness filters out the abstract, admitting only the concrete, while the unconscious tolerates the abstract. Why this should be I don’t know, but it seems like a possibility. Certainly it is a good question why the language of thought should be so removed from our consciousness.
 I say this for the sake of argument; actually it is not clear that we do perceive our language of communication. We perceive various sounds and marks with the senses, but it is another question whether we perceive words and sentences. These are more abstract categories than sounds and marks, more deeply psychological; and it may be that we bring these categories to external stimuli rather than perceiving them there. Indeed, it may be that we never really perceive (with the senses) words and sentences—we infer them from what we do so perceive (or impose them). So the language of communication may not as accessible to consciousness as we think.
 We need not suppose that bees engage in acts of speaker meaning, as characterized by Grice, which does require consciousness; it suffices for the point that they employ a system of communication whose nature is not given to them.