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<p>I couldn’t disagree more. You should be able to get to know a professor well enough in a single semester that they can write you a terrific, detailed, highly personalized recommendation letter. If not, something is wrong. And as a pedagogical matter, it’s always better to be challenged by more professors, who think about things in different ways, use different methodologies, bring different insights to bear, even if operating within the same discipline. I always tell my students that if you take three classes from me, it’s probably too much, you’re stifling your intellectual development. Two is fine; three is almost always too much.</p>