Disclaimer: The following is but a brief clarification on what the human brain does when one's behaviour is reinforced or punished. Thorough, exhaustive, and scholarly it is not.

Summary: Punishment, reinforcement, etc. of a behaviour creates an association in the mind of the affected party between the behaviour and the corresponding punishment, reinforcement, etc., the nature of which can only be known by the affected party. Take care when reinforcing or punishing others, as you may be effecting an unwanted association.

I've noticed the behaviourist concept of reinforcement thrown around a great deal on this site, and am worried a fair number of those who frequent it develop a misconception or are simply ignorant of how reinforcement affects humans' brains, and why it is practically effective.

In the interest of time, I'm not going to go into much detail on classical black-box behaviourism and behavioural neuroscience; Luke already covered the how one can take advantage of positive reinforcement. Negative reinforcement and punishment are also important, but won't be covered here.

Willard Quine described, in his article "Ontological Relativity" (Journal of Philosophy 65(7):185-212), his doctrine of the indeterminability of translation.  Roughly, this says that words are meaningful (a collection of words emitted by an agent can help predict that agent's actions), but don't have meanings (any word taken by itself corresponds to nothing at all; there is no correspondence between the word "rabbit" and the Leporidae).

In Quine's words,

Seen according to the museum myth, the words and sentences of a language have their determinate meanings. To discover the meanings of the native's words we may have to observe his behavior, but still the meanings of the words are supposed to be determinate in the native's mind, his mental museum, even in cases where behavioral criteria are powerless to discover them for us. When on the other hand we recognize with Dewey that "meaning. . . is primarily a property of behavior," we recognize that there are no meanings, nor likenesses nor distinctions of meaning, beyond what are implicit in people's dispositions to overt behavior. For naturalism the question whether two expressions are alike or unlike in meaning has no determinate answer, known or unknown, except insofar as the answer is settled in principle by people's speech dispositions, known or unknown.

Quine got my hackles up by using the word "naturalism" when he meant "behaviorism", implicitly claiming that naturalistic science was synonymous (or would be, if he believed in synonyms) with behaviorism.  But I'll try to remain impartial.  (Quine's timing was curious; Chomsky had demolished behaviorist linguistics in 1959, nine years before Quine's article.)

Quine's basic idea is insightful.  To phrase it in non-behaviorist terms:  If all words are defined in terms of other words, how does meaning get into that web of words?  Can we unambiguously determine the correct mapping between words and meanings?

Quine's response was to deny that that is an empirical question.  He said you should not even talk about meaning; you can only observe behavior.  You must remain agnostic about anything inside the head.

But it is an empirical question.  With math, plus with some reasonable assumptions, you can prove that you can unambiguously determine the correct mapping even from the outside.  In a world where you can tell someone to think of a square, and then use functional magnetic resonance imaging and find a pattern of neurons lit up in a square on his visual cortex, it is difficult to agree with Quine that the word "square" has no meaning.

You may protest that I'm thinking there is a homunculus inside the mind looking at that square.  After all, Quine already knew that the image of a square would be imprinted in some way on the retina of a person looking at a square.  But I am not assuming there is a homunculus inside the brain.  I am just observing a re-presentation inside the brain.  We can continue the behaviorist philosophy of saying that words are ultimately defined by behavior.  But there is no particular reason to stop our analyses when we hit the skull.  Behaviors outside the skull are systematically reflected in physical changes inside the skull, and we can investigate them and reason about them.

The more I tried to figure out what Quine meant - sorry, Quine - the more it puzzled me.  I'm with him as far as asking whether meanings are ambiguous.  But Quine doesn't just say meaning is ambiguous.  He says "there are no meanings... beyond what are implicit in... behavior".  The more I read, the more it seemed Quine was insisting, not that meaning was ambiguous, but that mental states do not exist - or that they are taboo.  And this taboo centered on the skull.

That seemed to come from a religious frame.  So I stopped trying to think of a rational justification for Quine's position, and starting looking for an emotional one.  And I may have found it.