What is Similarity and How Can Scientists Measure it?

Abstract

Which is closer to a dog: a cat or a fish? Easy! The cat is closer. What you may not have noticed here, is that we asked which is closer, not more similar. It does not matter which term we use because people usually understand that the term closer means more similar when used in questions like this. People often talk about similarity between objects as if this idea could be thought of as a distance between two (or more) items. It feels very natural to use the language of distance (words like closer, near, or far) to describe similarity. The tendency to understand similarity as a distance is useful to scientists because, as you know, it is very easy to measure distances as numbers (like measuring the distance between two points using a ruler). In this article, we will tell you how psychologists measure similarity and use those numbers to explore how the mind works.