What is a Counterexample? (and why philosophers use fictional examples)

This is a short lecture video explaining one of the most common and most powerful philosophical tools: the counterexample. Counterexamples are examples that are given to disprove a general claim. This video also explains how general claims centrally involving a concept--i.e., those claims about conceptual truths--can be proven false with the use of a fictional or even impossible counterexample.