"Every sentence has a subject and a predicate. In “Billy jumps,” “Billy” is the subject, and “jumps” the predicate. Basically, a predicate is anything that can describe or affirm something about a subject. A predicate can have more than one input. Suppose we define the predicate IsFanOf as follows: Let IsFanOf(x, y) be the proposition that x digs the music of rock band y. Then I can assert: IsFanOf(Stephen, Led Zeppelin), IsFanOf(Rachel, The Beatles), IsFanOf(Stephen, The Beatles), and ¬IsFanOf(Stephen, The Rolling Stones). We could even define TraveledToByModeInYear with a bunch of inputs: Let TraveledToByModeInYear(p, d, m, y) be the proposition that person p traveled to destination d by mode m in year y. The following statements are then true: TraveledToByModeInYear(Stephen, Richmond, car, 2017), TraveledToByModeInYear(Rachel, Germany, plane, 2014), and ¬TraveledToByModeInYear(T.J., Mars, spaceship, 1776). Defining multiple inputs gives us more precision in defining relationships. Imagine creating the predicate “AteWithAttitude” and then asserting: AteWithAttitude(lonely boy, spaghetti, gusto), ¬AteWithAttitude(T.J., broccoli, gusto), and AteWithAttitude(T.J., broccoli, trepidation). The IsFanOf predicate is identical to an isFanOf relation defined between sets P and R, where isFanOf ⊆ P × R. A relation can be defined as the set of ordered pairs, or tuples, for which a predicate is true."