The so-called "concrete" thinking of schizophrenic patients is undifferentiated thinking—thinking in which there is no differentiation between potentially concrete meanings and potentially figurative meanings. This "thought disorder" is not confined to some limited realm of experience comparable with the stratum of thinking in the normal adult, for in the deeply dedifferentiated patient there is no such well-defined stratum in his subjective experience. The disorder permeates his whole affective life, and his whole perceptual experience of himself and of the world around him.

Schizophrenia so severe as to involve a marked "thought disorder" of this kind is usually mentioned, in the psychiatric and psychoanalytic literature, in fatalistic terms, as if it were tantamount to incurability. With prolonged and intensive psychotherapy in a favorable milieu, however, it can be resolved.