The chimpanzee―who puts the two sticks together in order to get at the banana because no one of the two is long enough to do the job―uses intelligence. So do we all when we go about our business, „figuring out“ how to do things. Intelligence, in this sense, is taking things for granted as they are, making combinations which have the purpose of facilitating their manipulation; intelligence is thought in the service of biological survival. ― Reason, on the other hand, aims at understanding; it tries to find out what is behind the surface, to recognize the kernel, the essence of the reality which surrounds us. (…) Reason requires relatedness and a sense of self. ― (1955a: The Sane Society, New York (Rinehart and Winston, Inc.) 1955, pp. 169f.)
By intelligence, I mean an ability to manipulate concepts, but not to penetrate through the surface to the essence of things, to manipulate rather than to understand. This faculty of understanding, one might call reason, in contradistinction to manipulating intelligence. Reason indeed 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. You might say this kind of intelligence has the very same character of abstractifi-cation which our feeling and our sensing has. ― (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.)