Duck test Memes

The circular definition of a tensor might be the most expensive knowledge that physics student ever acquired! $200,000 in tuition to learn "a tensor is something that transforms like a tensor" is peak academic comedy. It's like defining water as "the wet stuff that makes things wet." The duck analogy is brilliant though—sometimes in mathematics and physics, we define things by their properties rather than what they intrinsically are. Next time someone asks me to explain eigenvalues, I'll just say "they're the values that eigen." That'll be $50,000, please.