In Chapter Three of The Soul, Moreland presents a number of arguments as to why "conscious properties/events are mental, not physical" (p. 78). Among other things, Moreland contends that mental states are not physical because they exhibit certain characteristics that physical objects do not. For instance, mental states are often directed toward an object (they can be "about" something), they can only be possessed by the individual having them, and they lack certain qualities, like spatial extension and location, that physical objects exhibit. Employing the law of identity--that x and y are identical only in such cases in which whatever is true of x is also true of y and vice versa--we must conclude, therefore, that mental states are not physical in nature.
What does this conclusion have to do with the problem of explaining the origin of human language? I shall explain. On pages 77-78 of his book, Moreland defines a number of different types of conscious states. One of these is thought. According to Moreland, "[a] thought is a mental content that can be expressed in a sentence" (p. 77). The word sentence implies language. In other words, a thought is a mental entity that is represented by language. Thus, it follows that there is a close connection between language and thought.
Here is the difficulty. Evolutionary linguistics treats language as a physical phenomenon. This is not surprising for neo-Darwinian evolution, which evolutionary linguistics presupposes, is based on materialism--the belief that the material or physical is the only thing that really exists. Consequently, from the viewpoint of evolutionary linguistics, language is a matter of physical characteristics and processes--for example, the position of the larynx (which is important in the production of speech sounds), or the electro-chemical processes taking place in the left hemisphere of the brain which are associated with language processing. Thus, to explain how human language emerged, one merely needs to explain how these physical characteristics and processes came into being. However, if language is closely related to thought, and thought is not physical in nature, then an adequate theory of the origin of human language would need to explain how something (putatively) physical in nature came to be connected to something that is not physical in nature. Indeed, such a theory would need to accommodate the existence of something that is nonphysical or nonmaterial in nature (i.e., thought), but since evolutionary linguistics ultimately is predicated on materialism, it cannot do so.
Note that this problem does not arise if we reject the materialism presupposed by evolutionary linguistics. If nonmaterial properties and/or entities can exist, then it would be possible for language to be somehow connected with something nonmaterial, namely human thought. The nature of that connection might still be obscure, but at least such a relationship could exist.
In short, if Moreland is correct in contending that mental states are not physical in nature, and if language is closely linked to thought, which is a mental state, then evolutionary linguistics is incapable of providing a satisfactory explanation of the origin of human language, as it cannot explain the connection between language and thought since it presupposes materialism.
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