Is it the case that despair, even a secret one, requires a heart? Or does despair only require a heart to feel it? If the Despiser doesn't have a heart then obviously he can't feel despair, assuming he can have it in secret concealed even from himself.Covenant remembered the sources of the Despiser’s frustration, the roots of his accumulating, minatory fury. He recognized the Despiser’s own secret despair, concealed even from himself, and enacted on the beings around him instead.
If the Despiser has a secret despair, does he also have a secret heart concealed even from himself? Is this why he told Linden in ROTE that he doesn't have a heart - he has one but he himself doesn't even know about its existence?
It is possible, in human psychology anyway, to have an emotion and not know it or feel it - this is called repression - and then unknowingly to project that emotion onto others. In Foul's case, the emotion of despair is projected onto others, by causing them to experience it for him, and then rationalized as a ploy to eventually escape from his emprisonment.
I call it a rationalization because other ploys might work just as well, but something in the Despiser's psychology leads him to this particular ploy and so, as a form of self-concealment, he has to justify it somehow.
It may be the case that psychology does not require the concept of a "heart," but it does require the concept of an emotional center loosely known as the heart.
If the Despiser has a form of despair within him, then why does he choose to conceal its existence even from himself?