ABSTRACT
Same—different is an exceedingly simple judgment from the human point of view, so basic to our theorizing that we have difficulty describing events in the world without it. We use it unthinkingly, both in describing our own behavior, where the description may be correct, and in describing the behavior of lesser species, where it may be less correct. For instance, in watching a pigeon select grain from a set of particles, we rather automatically describe the behavior in terms of same—different judgments. We assume that the bird judges each new particle to be the same as one it has already eaten (in which case it eats the particle), the same as one it has already rejected (in which case it avoids the particle), or different from either (in which case it tries out the particle). Although same—different is obviously vital to this account, an alternative account can be given in which it plays no role whatever—fortunately, for there is reason to believe that pigeons are incapable of same—different judgments.
