There are several forms of symptom coherence. Some symptoms are necessary because they serve a crucial function (such as depression that protects against feeling and expressing anger), while others have no function but are necessary in the sense of being an inevitable effect, or by-product, caused by some other adaptive, coherent but unconscious response (such as depression resulting from isolation, which itself is a strategy for feeling safe). Both functional and functionless symptoms are coherent, according to the client's own material.