 Many mental states or acts (some think all mental states or acts) are intentional in that they are about something or other. You do not simply think; you think something. You do not merely believe or desire; you believe or desire something. This something that you think, believe, desire or, for that matter, hope, fear, expect, anticipate, and so on, is the content of the thinking, believing, desiring, hoping, fearing, expecting and anticipating. Content externalism—sometimes known as semantic externalism, since content is sometimes known as semantic content—is externalism about the content of mental states or acts.