Concept formation is the process of integrating a series of features that group together to form a class of ideas or objects.

## Concept formation

### Ayn Rand's formulation

The first step in concept formation, called differentiation, is to isolate two or more things as belonging together, as units of the same class. Where many theories of concept formation hold that such isolation begins by noticing degrees of similarity, Objectivism holds that it starts by noticing degrees of differences. At the perceptual level, everything is different; however, somethings are more different from others. The difference between two tables, for instance, is less than the difference between a table and a chair. Because two tables are less different from one another when contrasted against a third object, we group them together as units, as members of a group of similar objects.

Ayn Rand defines similarity as: the relationship between two or more existents which possess the same characteristic(s), but in different measure or degree. Similarity is a matter of measurement. Going back to the table versus chair example, the difference between tables is a quantitative one-we can easily stretch one table into another, so we call them similar. The difference between tables and chairs, on the other hand, is qualitative, so we distinguish between these as belonging to another group. Of course, at a broader level, even the difference between tables and chairs is quantitative-with enough stretching and pulling one could turn a chair into a table as well. However, the point is that the table-to-table stretching is much less than the table-to-chair stretching, so we consider one quantitative and the other qualitative.

The second step of concept formation, integration, is based on a process Ayn Rand called measurement omission. In this step, we combine or integrate the units into a new, single mental unit by eliding the quantitative differences between the two units. We retain the characteristics of the units, but we elide the particular measurements-on the principle that these measurements must exist in some quantity, but may exist in any quantity. For example, when forming the concept table we retain the distinguishing characteristics-a flat, level surface and supports-but omit the particular measurements of those features.

Based on this two step process, Ayn Rand defined concepts as: a mental integration of two or more units possessing the same distinguishing characteristics, with their particular measurements omitted.