-The same general principles of reasoning apply to psychological theories, even though psychology is a much more difficult subject matter and our available theories are correspondingly much poorer and vaguer. There's no way to make precise quantitative predictions about a human's behavior the way we can about the movements of the planets, but we still know _some_ things about humans, which get expressed as high-level generalities that nevertheless admit many exceptions: if you don't have the complicated true theory that would account for everything, then simple theories plus noise are better than _pretending not to have a theory_. As you learn more, you can try to refine more complicated theories that explain some of the anomalies that looked like "noise" to the simpler theory.
+The same general principles of reasoning apply to psychological theories, even though psychology is a much more difficult subject matter and our available theories are correspondingly much poorer and vaguer. There's no way to make precise quantitative predictions about a human's behavior the way we can about the movements of the planets, but we still know _some_ things about humans, which get expressed as high-level generalities that nevertheless admit many exceptions: if you don't have the complicated true theory that would account for everything, then simple theories plus noise are better than _pretending not to have a theory_. As you learn more, you can try to pin down a more complicated theory that explains some of the anomalies that looked like "noise" to the simpler theory.
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+What does this look like for psychological theories? In the crudest form, when we notice a pattern of traits that go together, we give it a name.