Aristotle's theory of universals

universals are the characteristics or qualities that ordinary objects or things have in common.

They may also be at varying degrees of age, which will affect their color, but they will all share a universal "appleness".

A common defense of Aristotle's realism is therefore that we should not expect universals to behave like ordinary physical objects.

Aristotle argued that people form concepts and make generalizations in the manner of a young child, who is just on the verge of grasping a generic concept such as human being.

In his view, the child is gathering his or her memories of various encounters with individual humans, searching for the essential similarity that stands out, on reflection, in every instance.

When the child grasps the concept of a human being, he or she has learnt to ignore the accidental details of each person's past experiences and individual differences, and has paid attention to the relevant quality that they all have in common, namely, humanity.