Word and Subject
The advent of language on our planet changed the natural history of consciousness. Before language existed animal consciousness was confined to sensation, perception, memory, emotion, and will—extensive but not exhaustive features of mind. What went through an animal’s mind was limited by these forms of basic consciousness—sights and sounds, smells and tastes, fear and contentment: but no words went through any animal’s mind—consciousness was a language-free zone. Consciousness may have been rich and vivid but it was not a verbal cacophony. Then language evolved, quite recently (less than 200,000 years ago by most estimates). Before long human consciousness was alive with words—with inner babble. Just think of how much of your waking life is consumed by words: you talk to yourself all day long. Human consciousness is silent soliloquy.  When you see a person walking quietly down the street you can be sure she is talking to herself a mile a minute. This is an interesting natural fact: the way language has colonized consciousness, transforming it. We still have the old forms of consciousness, but we also have this new form—linguistic consciousness. No doubt it is accompanied by an extensive linguistic unconscious, but the point I want to focus on is the presence of language to everyday human consciousness. What it is like to be a modern human is largely constituted by our consciousness of language. It is an inescapable part of what we are—we are verbal souls.
What concerns me is the existential condition this places us in (“existential linguistics”). Sartre said that we are always conscious of our freedom and that this conditions our entire outlook; I am noting that we are always conscious of our nature as speakers (inner and outer). Freedom produces anxiety, according to Sartre: what does language produce? What does all that talking do to us? I suggest that it robs us of peacefulness: the incessant inner monologue is just so frantic and frenzied (I am putting aside intermittent external speech). We never get a moment’s respite from our inner voice (sometimes from outer voices). Only in sleep do we fully escape language, and even then dreams can be verbally laden. It is just very hard to turn the inner voice off. Sometimes we can be distracted from it or slow its activity, but it is always waiting to stride back in and buttonhole us. Animals can live in relative peace, seeing, smelling, tasting, hearing—they are not troubled by that urgent voice within (and often the inner voice is not saying soothing things). They have, or can have, a tranquil consciousness, but in linguistic beings like us there is a continuous assault on tranquility. It takes effort to quiet this voice (meditation, sport, sex): the inner speaker demands to be heard. And the sheer rapidity of inner speech adds to its hectic phenomenology: so many words coming so quickly. If you had to hear that much speech coming through your ears, it would drive you mad. There is nothing calming about human linguistic consciousness—there is something here that we feel the need to escape. That “little voice in the head” is seldom a source of peace and is never ignorable. A break from it would be nice.
In addition human language is complex, a formidable formal object, however naturally it may slip off the inner tongue. Processing it calls for substantial mental resources: the brain must be hyperactive in order to service the furious stream of speech. Accordingly, we do not experience ourselves as linguistically simple. Just consider the complexities of grammar and the extent of vocabulary: the bigger your vocabulary the more voluble your inner speech is apt to become. All that choice, subtlety, and nuance—it’s psychologically challenging. Thus we experience ourselves as complex and intricate entities: for we possess a language faculty of endless potential and elaborate architecture, consciously so. It’s not like having a pleasant feeling of satiation in the stomach area. Animals are not subjected to this weight of complexity; their inner lives are simple and straightforward in comparison.  And it’s not that there exists some noble savage deep in the jungle untroubled by internal chatter: all humans are subjected to the barrage of language—its unrelenting presence to consciousness. Language by its nature occupies our consciousness to an extraordinary degree. It consumes our attention and shapes our experience. And it just won’t shut up. We can’t choose to turn it off for a few hours, thus regaining our pre-linguistic animal past; it is importunate to a fault. You can close your eyes and block up your ears, but you can’t cut yourself off from inner speech—it just keep jabbering away, with or without your consent. And it is not always scintillating, that inner voice, often merely obsessive and distressing. It can lead to insomnia, depression, maybe even madness. 
But there is a third aspect to word consciousness that is at least as powerful as the first two: inner language has made us much more introspective than we would otherwise be. It has caused us to be inwardly directed, precisely because inner speech is inner. Attending to the voice within makes us less attentive to other things—such as what is going on around us or other people. We have a tendency to listen too closely to the inner voice and not look around us (consider the pose of Rodin’s The Thinker). There are two sides to this inwardness. First, we simply focus more on the inside than on the outside: we are inward-looking beings, intent on what passes through our own consciousness. Animals don’t have this source of inner interest to compete with outer awareness, but we are pensive and self-obsessed by nature—constantly listening to our inner verbal performances. Language makes us live inside our heads. The other aspect is epistemic: the inner voice has too much influence over our beliefs and attitudes. What it chooses to ramble on about, obsess over, and insist upon has an inordinate role in shaping our view of the world; and it makes us particularly prone to wishful thinking, paranoia, and delusion. Inner speech is a kind of self-generated propaganda, biased and self-serving; and it is with us always. We need the fresh air of external input—from the world or other voices. The inner voice is just too persuasive, too silver-tongued. Surely an enormous proportion of the world’s problems stem from this aspect of word consciousness: we are too in thrall to what our inner voice is telling us–so proximately and persistently. Thus we are abnormally inner-directed and irrationally swayed, because of the words that filter constantly through our minds. Language has done this to us. In language users the natural history of consciousness has reached a distinctive stage: it pullulates with a torrent of verbiage. Words, words, words. No doubt this has its advantages, but it is a question whether it is conducive to wellbeing. There is something unique it is like to be human—to have a verbally saturated consciousness—but it has its downside. Language has reconfigured consciousness and we have to live with the result. 
 This is not a trivial consequence of having a language, since one can imagine beings equipped with language who consign it to the periphery of awareness, using it only rarely and quite able to interrupt it. But in humans language has taken over the premises: it is apt to fill every waking moment and sometimes seems to have a will of its own. We are condemned to language (to use a Sartrean idiom).
 I am not saying that faculties like vision or even digestion are simple, but they are not evidently complex in the way language is: language displays its complexity on its face—as is obvious when trying to learn a second language. No doubt this is (partly) why we tend to place ourselves above animals in the league of sophistication.
 Disorders of internal speech ought to be a psychiatric subject in its own right—a malady to which animals are not subject. There cannot be voices in the head if there is no language for them to speak.
 Remember that evolution doesn’t care if pain causes unhappiness so long as it aids in survival. Language might be a good survival tool while bringing a measure of discontent or disquiet in its wake (it might also bring some consolations—poetry, jokes, conviviality). Is part of the appeal of music its ability to displace the inner voice?