Reason is the capacity to recognize the unreality of most of the ideas that man holds, and to penetrate to the reality veiled by the layers and layers of deception and ideologies. ― (1962a: Beyond the Chains of Illusion. My Encounter with Marx and Freud, New York (Simon and Schuster) 1962, p. 179.)

Reason operates only if we are related to what we think about. If we are unrelated to it, then we can do nothing but to manipulate. We can weigh and count and figure and compare factors. ― (1991e [1953]: Modern Man’s Pathology of Normalcy, in: E. Fromm, The Pathology of Normalcy. Contributions to a Science of Man, New York (American Mental Health Foundation) 2010, p. 64.)

Reason is man’s faculty for grasping the world by thought, in contradiction to intelligence, which is man’s ability to manipulate the world with the help of thought. Reason is man’s instrument for arriving at the truth, intelligence is man’s instrument for manipulating the world more successfully; the former is essentially human, the latter belongs to the animal part of man. ― Reason is a faculty which must be practiced, in order to develop, and it is indivisible. By this I mean that the faculty for objectivity refers to the knowledge of nature as well as to the knowledge of man, of society and of oneself. If one lives in illusions about one sector of life, one’s capacity for reason is restricted or damaged, and thus the use of reason is inhibited with regard to all other sectors. Reason in this respect is like love. Just as love is an orientation which refers to all objects and is incompatible with the restriction to one object, so is reason a human faculty which must embrace the whole of the world with which man is confronted. ― (1955a: The Sane Society, New York (Rinehart and Winston, Inc.) 1955, p. 64.)