The concept of similarity is necessary and useful, though tricky to understand fully.

Cooking and leading call up some of the same psychological mechanisms.

There is value in asking unusual questions, especially if they lead to more questions.

Nothing is known. –Francisco Sanches (16th Century) Compared to what? –Herbert Stein (more recently)

Nothing is known. –Francisco Sanches (16th Century)

Compared to what? –Herbert Stein (more recently)

Similarity: A false but necessary god

How similar is a cat to a dog? Or, should we ask how similar a dog is to a cat? How different is one from the other? Amos Tversky (1977) showed that it matters a great deal how the question of similarity is asked. Psychologists and neuroscientists have much to say about how the mind-brain construes and computes judgments of similarity, often intuitively, spontaneously, and without effort (Medin et al. 1993). Research on how we perceive similarity is all the more important because philosophers and other masters of the art of deduction have banged their heads against the wall trying to put judgments of similarity on a logically coherent foundation. Goodman (1972) famously asserted that similarity is an indeterminate construct. It cannot get off the ground without an application of massive background knowledge and assumptions that must be accepted even if they cannot be fully justified.

Our intuitive judgments often reveal the background on which they stand. When we say Joey looks just like his father, we reveal how we perceive other son-father pairs. When we compare cats and dogs, we reveal the breadth of the context in which we consider this similarity judgment. When we judge cats and dogs to be similar, we are probably thinking about a wide world of animals, perhaps all vertebrates; when we judge them to be different, we might be focused on domesticated mammals.

Occasionally, a question comes along that does not call forth intuitive judgment. We have to put our........

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