In the previous chapter we formulated a stance that enables us to ask what the relation is between the physical sciences and the truths expressed in our mental language while carrying the minimum of metaphysical baggage. We avoid all ontological presuppositions about mental entities by tentatively treating all sentences of the mental language as containing no referential terms. Thus for at least the time being we absolve the scientist from the responsibility of discovering physical events, states or processes which deserve to be called thoughts, ideas, mental images and so forth. No entity on his side of the fence need line up with mental language in such a way that we would say he has discovered what thoughts are, or isolated a mental image or even the experience of having-a-mental-image. We have the mental language, and since the suggestion that all the things we say in the mental language might be false is incoherent, we also have the truths expressed in mental language. The task is to relate these truths to the scientific corpus, and further to explain the

relations. Since we cannot very well claim to have explained a mental phenomenon if we are unable to say (in the scientific language of our explanation) when a sentence heralding the occurrence of the phenomenon is true and when not, our task will involve at least this much: framing within the scientific language the criteria – the necessary and sufficient conditions – for the truth of mental language sentences. At this point we face a very general argument designed to show that this is impossible, that no criteria for mental truths can be expressed in the language of science.