Swiss psychiatrist Eugen Bleuler, who coined the term schizophrenia, identified affect, association, ambivalence and autism as the so-called “Four As” of negative symptom schizophrenia. Latter-day observers have sometimes added alogia, anergia, anhedonia, and apathy/amotivation to the original list.

Negative symptoms, as classically associated with schizophrenia, refer to the absence of normal function (hence, they are “deficit” states), as contrasted with positive symptoms (that is, the excess presentations of otherwise normal brain functions). In that sense, negative symptoms also differ fundamentally from depression insofar as the latter represents a kind of positive symptom, one characterized by the “feelingful” presence of emotions (anguish, despair) – quite different from the emotional vacancy of flat (rather than sad) affect. The schizophrenia literature often refers explicitly to “the deficit syndrome.”