Typicality is routinely invoked in everyday contexts: bobcats are typically short-tailed; people are typically less than seven feet tall. Typicality is invoked in scientific contexts as well: typical gases expand; typical quantum systems exhibit probabilistic behaviour. And typicality facts like these support many explanations, both quotidian and scientific. But what is it for something to be typical? And how do typicality facts explain? In this paper, I propose a general theory of typicality. I analyse the notion of a typical property. I provide a formalism for typicality explanations, and I give an account of why typicality explanations are explanatory. Along the way, I show how typicality facts explain a variety of phenomena, from everyday phenomena to the statistical mechanical behaviour of gases. Finally, I argue that typicality is not the same thing as probability.

2.  An Analysis of Typicality

3.  Typicality Explanation

3.1.  Examples of typicality explanations

3.2.  A formalism for typicality explanation

3.3.  An account of explanatory typicality facts

4.  Differences between Probability and Typicality

4.1.  Explanatory differences

4.2.  Formal differences

4.3.  Metaphysical differences