 Oh, a functionally equivalent response, folks. It's a response that's functionally equivalent to another. In other words, a response that produces the same reinforcer or the same outcome as another response. So have you ever tried to turn on a light switch? You know, you typically walk into a room and you go, you flip the light switch. You can even flip it this way, or you can do it this way. You can do it with your butt. You can do it with your ears, which that hurts. Don't ask me how I know. All responses are functionally equivalent. They produce the same thing. This is why behavior analysis is considered a molar field, not a molecular one, because we don't really give two hoots about individual responses unless we're worrying about like topography or something or there's reason to. All we really care about is the function of a response. What does it get you? And in any behavior that gets you to that function, we can strengthen it. Reinforcers strengthen classes of responses. Those classes of responses are all functionally equivalent. It's a large to it.