Nate Charlow makes fun of an intentionalist theory of meaning here. Recent readers will be pleased to learn that there is a da Vinci angle.
The serious issue is whether an "intentionalist" theory of meaning makes sense. Everyone seems to think this is politically important because it is tied to whether a constitution should be interpreted as its framers would have done, or should evolve like a "living tree."
Intentionalism, as a philosophical matter, is the idea that the meaning of an utterance depends on a psychological intention of the speaker. The basic argument against such intentionalism is as follows:
1. Suppose that "what the speaker intended" means "what the speaker intended to say."
The difficulty with this version of intentionalism is that what the speaker intended to say must itself be a proposition. So we are no closer to a theory of meaning. If I say "Michelangelo painted the Mona Lisa", I can correct myself by saying that I meant to say "Leonardo." I misspoke, and everyone other than strict Freudians will let you get away with a misspeaking now and then. But if I said "Leonardo painted the Mona Lisa", and you want to know what I meant, then saying I meant what I intended to say can't advance things any further, since what I intended to say was "Leonardo painted the Mona Lisa."
On this view, what we say and what we intend to say will (normally) be the same. But that is just because we are competent speakers. It doesn't define what we mean as what we intend to mean (since that definition would be circular).
2. Suppose that "what the speaker intended" means "what the speaker intended to accomplish", i.e., the (non-linguistic) intended effect of the utterance.
This version of intentionalism at least avoids circularity. But it has the problem that two speakers can say the same thing, intending different effects, or say different things, intending the same effect. For instance, I might yell, "Fire" in a crowded theatre as a distraction so that my confederates can more easily rob a bank next door, while someone else might take up my call in order to save the lives of the theatre goers. We mean the same thing, but are trying to accomplish different things.
At least in typical contexts, when we make a statement of fact, we want our hearers to believe a certain fact that we believe (or that we nefariously want the hearer to believe even though we don't believe it). And, IMHO, belief of a fact is non-linguistic, since animals can believe facts and foreigners can believe the same facts we believe even though we don't understand each other's language. The fact can only be described in language, of course, but that doesn't mean that the fact is linguistic.
But sometimes we don't even care whether the other person comes to believe the fact we are describing (Martin Luther before the Diet, for instance). Whether we care about whether the listener believes us cannot determine the meaning. And we aren't always communicating facts.
So what does this have to do with jurisprudence?
The political valence of this relatively-arcane issue is that American conservatives tend to prefer an "original intent" version of Constitutional meaning. (Canadian conservatives have never been as sure about this, since the Judicial Committee of the Privy Council liberated the provinces from what was originally intended to be a very centralist constitution, and since the Charter was written under the auspices of Pierre Trudeau and Jean Chrétien.)
Linguistic philosophy might help us with this problem. But jurisprudence isn't interested in the "meaning of words" in general, but their meaning in the context of particular social practices, notably litigation.
Most litigation involves the application of legally-binding texts (contracts, trust instruments, regulations, statutes or constitutions) to a dispute over the availability of a remedy (damages, declarations of invalidity of a subordinate legal instrument or injunctions). In constitutional litigation, the issue is whether some constitutional text (e.g., limiting the authority of Congress to "Interstate Commerce" or prohibiting the state from depriving a person of life, liberty or property "without due process of law") is inconsistent with some statutory text (e.g., a federal law prohibiting "partial-birth" abortion).
So when we interpret (or "construct") a constitutional provision, what we are really doing is determining consistency: is what the statute does consistent with the norm the constitution sets forth? How much does intention and meaning, as the philosophy geeks have elucidated them, come into this practice? The answer is not very much.
The ordinary case in which intention and meaning don't line up ("I meant 'Leonardo'") can't apply to constitutions. The framers intended to write what they wrote. This ordinary issue of intention arises in lesser legal documents, like wills and contracts, and even statutes, but no one doubts that constitutions are carefully written in this sense at least. No historian is going to come up with proof that the Fourteenth Amendment contains a typo.
So we can be reasonably sure that when the framers of the Fourteenth Amendment prohibited depriving a person of property without due process of law, they meant to prohibit depriving a person of property without due process of law. But we don't know whether this allows zoning bylaws, or, if it does, whether it requires that the zoning authority provide notice to affected property owners before it makes its decisions.
In old constitutional documents, the issue of linguistic change may be important. "Misdemeanour" undoubtedly meant something different in the eighteenth century than it does now. But it is easy to overstate this. Conceptions of "cruel and unusual punishment" have changed vastly since the eighteenth century -- but this change is not primarily linguistic. A "cruel" punishment, then as now, meant one that was unacceptably harsh for a civilized society. If you say what you mean, then what you intended to say is what the relevant linguistic community understands you to say. Since we are part of the relevant linguistic community when it comes to recently written legal texts, "intention" at this level helps us not at all.
What about what the writers of the document intended to do when they said what they said? A historian could definitely help us with that. The difficulty is that this is not obviously relevant to the social practice of litigation. The framers may not have meant to do anything in particular with the resolution of the particular conflict represented by the litigation. They may have had no idea of how to resolve it, or different ideas. Even if they all would have thought that a life sentence for stealing a slice of pizza would not be "cruel", we are not obliged to agree with them, even if we try to be true to their meaning of the words they used. By "cruel", they meant really, genuinely cruel. So do we. When we disagree about what is cruel, we are not engaging in a linguistic disagreement.
What we are doing is not (at least not primarily) a linguistic exercise of divining meaning, or a historical exercise of divining pragmatic intentions, but a logical/factual inquiry into consistency. We are trying to figure out whether, in fact and in logic, the higher-order norm set out in the constitution is consistent with the lower-order norm set out in the statute. That question of consistency involves evidence and argument, which is a good thing, since that is what litigation is about.
In addition to vertical consistency between higher-order legal texts and lower-order texts, a legal system needs consistency between earlier and later decisions. So every finding that a lower-order norm is (or is not) consistent with the constitution in turn becomes a part of the constitution. This isn't just a matter of convenience or a traditional accretion on the original "plain" meaning (that Protestant holy-of-holies). It is the requirement that the legal order be coherent.
The bottom line is, once again, that legal "interpretation" is not really about "meaning" and therefore is not about "original meaning." It is about a particular social practice -- litigation -- and if we are worried about constraining judicial power (as we should be), we should seek the constraints in the limits of that social practice.
Update: Brian Leiter has pointed to Richard Rorty's most recent thoughts on meta-philosophy. Rorty is OK with the idea that no two utterances ever mean the same thing. If you are OK with that, you don't really need a theory of meaning, just a sociobiology/history of communicative behaviour.