RT needs to be seen in the context of reasoning about programs. Suppose we want to define a constant function f such that f x = 0. Under strict semantics in a

RT needs to be seen in the context of reasoning about programs. Suppose we want to define a constant function f such that f x = 0. Under strict semantics in a total language, you're fine. Under strict semantics in a partial language f undefined blows up. So constant functions, the simplest kind possible, don't even exist! OMGWTFBBQ! You can still reason about programs, but at a very low-level, i.e. on operational semantics. RT is high-level reasoning. Math, which does have constant functions, seems pretty successful, so we'd like a slice of that cake, please.