First of all, the virtue of rationality is manifested only in what in the broadest sense counts as reasoning; in this way, rationality differs from many other virtues, which are also manifested in one's feelings and actions (as well as in one's reasoning).

Is rationality a value?

Rationality is itself a kind of value, and more specifically, a virtue (Chapter 6) that supervenes on the mental (Chapter 7). ... Wedgwood says that rationality, while supervening on the internal, has an external “aim”: correctness (Chapter 9). That's why rationality matters and is not just a “pretty pattern” in the mind.

How do you define rationality?

Rationality is the quality or state of being rational – that is, being based on or agreeable to reason. Rationality implies the conformity of one's beliefs with one's reasons to believe, and of one's actions with one's reasons for action.