This post is a summary of the chapter "Mentalese" from the book "The Language Instinct" written by the eminent linguist Steven Pinker. This chapter deals with the question - Do we think in language? What is the language of thought?
According to the Sapir-Whorf hypothesis, language shapes our model of the world. For example, forms of addressing the listener are different in many languages depending on age or relation. The demands made by the language might influence the speakers to regard the listener with respect. In languages such as Hindi or Tamil, formalness is frequently employed in day-to-day communication. This is in contrast to other languages such as Malayalam, in which formalness is not commonly employed, in spite of the presence of formal and informal forms of address.
Pinker challenges this hypothesis in various ways. First, it is difficult to test this hypothesis because of the circular nature of the existing experiments. A subject can only be evaluated based on what he/she speaks. Second, the 'fact' that the Eskimos have hundreds of words for snow is nothing but an urban legend. According to one survey, the actual number is less than ten. So the Eskimos regard snow similar to the way others do, contrary to what the hypothesis can be taken to mean. Third, there are many beings that cannot speak but possess the faculty of thought: deaf people, babies, animals (, plants?). Fourth, many a time, even though we have a thought in our mind, we struggle to express it clearly. This can be due to two reasons: (1) lack of command over languages, or (2) lack of devices in language to convey our thoughts. Movies are arguably powerful means of art than, say, poem or music, because of the use of audio as well as video. Fifth, it is possible for us to transform (e.g. rotate or zoom in) an image in our minds without speaking about the process loudly. All of the above suggest that English or any other spoken language is not the language of thought.
Pinker claims the language of thought (a.k.a. Mentalese) to be on a level that is different from spoken languages. All thinking creatures use this language to think. Since only human beings possess the ability to talk, there is a program, similar to a compiler for programming languages, in the human brains that converts the high-level Mentalese to the low-level English.