The way to identify and think about abstractions is through contrast and comparison. Pure abstractions will always fit into a four-point comparative scale:

1. Things that are identical
2. Things that are similar
3. Things that are dis-similar
4. Things that are opposites

Although no two objects are precisely alike or precisely opposite, they can be alike enough, or opposite enough (compared to similar or dissimilar), so that we can reasonably apply the scale.

Given this, in order to understand what is meant by "hot" (or what hot is), we could compare one object that is "hot" to a second object that is also "hot". However, in this case, if both are "hot" (identical), we don't know much more about what "hot" actually is (or is not) than we did before. There is no way to distinguish between two identical "hot"'s.