Descartes may have made a lot of mistakes, but he was right about this: you cannot doubt the existence of your own consciousness. That's the first fe… - John Searle

The general nature of the speech act fallacy can be stated as follows, using “good” as our example. Calling something good is characteristically praising or commending or recommending it, etc. But it is a fallacy to infer from this that the meaning of “good” is explained by saying it is used to perform the act of commendation.

There is probably no more abused a term in the history of philosophy than “representation,” and my use of this term differs both from its use in traditional philosophy and from its use in contemporary cognitive psychology and artificial intelligence.... The sense of “representation” in question is meant to be entirely exhausted by the analogy with speech acts: the sense of “represent” in which a belief represents its conditions of satisfaction is the same sense in which a statement represents its conditions of satisfaction. To say that a belief is a representation is simply to say that it has a propositional content and a psychological mode.

In many cases it is a matter for decision and not a simple matter of fact whether x understands y; and so on.