 This illustrates how quite involved reasoning can be expressed in a simple syllogistic-like language. The inference is valid, but one has to think a bit to see  that.[42]  A main feature of most of these fragments is that, in addition to having explicit complete axiomatizations, validity in them is decidable, in contrast with first-order logic. This also holds for some fragments with quantifiers that are not FO-definable. Like the monotonicity calculus, the study of syllogistic fragments is part of the enterprise somewhat loosely called natural logic, resulting in well-behaved subsystems of more familiar logics, in the sense of being both closer to natural language and computationally more tractable; see Moss (2015) for a  survey.[43]