Full Idea
A defence of the language of thought has to be an argument that believing and desiring are typically structured states.
Gist of Idea
Belief and desire are structured states, which need mentalese
Source
Jerry A. Fodor (Psychosemantics [1987], p.136)
Book Reference
Fodor,Jerry A.: 'Psychosemantics' [MIT 1993], p.136
A Reaction
A structure is one thing, and a language is another. Both believings and desirings can be extremely vague, to the point where the owner is unsure what is believed or desired. They can, of course, be extremely precise.