In effect, a Cartesian subject is not capable of learning and using language. Therefore, philosophy based on a Cartesian subject is useless. Benjamin's argument will now be assessed by focusing on the three main arguments that he makes about the qualities of language for a Cartesian subject.

             The first quality that Benjamin notes is that language would have to be self-taught. As Benjamin (29) says, "You cannot have learned it from other people because you're assuming that there aren't any." You also cannot assume that you just know the language, because you may just be being tricked into believing that you know the language. This argument is valid. In Descartes philosophy, a Cartesian subject is a lone subject of consciousness. This subject cannot look outside themselves for certainty, because everything outside themselves could be false. Without doing so, there is no way to be certain that the words being used have certain meaning. Descartes first certainty where a person cannot doubt their existence because they are thinking requires language. A person has to think this and understand this, to know that it cannot be doubted. However, this conclusion is not actually certain because the words being used do not have certain meaning. If Descartes' argument that what might be false must be accepted as false, than the meaning of the words must be accepted as false. This makes his first assumption meaningless. This shows that Benjamin's first argument against Descartes is valid.

             The second argument Benjamin makes is that the language would have to private. This is based on the idea that a lone subject cannot determine the meaning of language from others or the world around them. This leaves the possibility that people teach themselves language based on past experience. Benjamin uses the meaning of the word doubt to describe this. He notes that a person might experience a feeling of doubt in the past and then create the word and attach meaning to the experience.