In earlier classes, we mentioned the idea of mental states being “intentional/representational” or about things. And we also mentioned a term “intensional” that philosophers sometime use (spelled with an “s” where the other has a “t”). I said that these concepts are connected but different. I also said that not everyone uses these words in exactly the same way. So I can’t show you official definitions that every philosopher who uses these words agrees with.
Still I can help you get a handle on what they mean, and the differences in how they’re used.
“Intensional” (with an “s”) is contrasted to “extensional”.
“Extension” is sometimes used to talk about how much space an object takes up (we say the object “is extended”). Ignore that usage for this discussion. It’s not relevant here.
The usage we want to focus on is when philosophers talk about the extension of some words or properties. That’s being contrasted with their meaning or intension. We say that some words or properties are extensionally the same when they happen to characterize or apply to the same members. For example, let’s suppose that as a matter of fact, all the lawyers in North Carolina play golf, and everyone who plays golf is a lawyer. It didn’t have to be that way; there’s not a rule or anything that prohibits plumbers from playing golf, or which says lawyers have to golf. But as a matter of fact, that’s how it turned out. Then we would say that the words “golfer in North Carolina” and “lawyer in North Carolina” are co-extensional or have the same extension (their extension is the set of objects they apply to). But these words don’t have the same meaning. That’s why it didn’t have to be that way. On the other hand, perhaps the words “lawyer” and “attorney” do have the same meaning. (Some people say there are subtle differences, but I don’t know what they are. Let’s pretend they’re perfect synonyms and mean the same.) So then “lawyer” has the same meaning or intension as “attorney,” but only the same extension as “golfer.”
Some writers also talk about the “extensions” of other kinds of words, including names and sentences. Some also talk about the “intensions” of these words. There are different views about what the extensions of these other expressions should be. (Notably, the philosopher Frege argued that the extensions of sentences are truth-values.)
On top of these multiple meanings and words with similar spellings, there’s an extra twist that the term “intension” has slightly shifted its meaning over time. Consider predicates like “is water” and “is H2O.” Arguably, these predicates don’t have the same meaning. At least, one can learn the competent use of both of these expressions without realizing they apply to the same liquid. On the other hand, as we’ll see in later classes, nowadays many philosophers think that the essence of water turns out to be being made of H2O. So necessarily, if something is water it’s H2O, and vice versa. Now, the way the technical term “intension” was first used, if two predicates had different meanings, then they had different intensions. But sometime between the 1940s and 1970s a newer usage evolved, so that a philosopher with the modern view of water/H2O would say that “water” and “H2O” have the same intension, after all, because in every possible world where something is water, it’s also H2O and vice versa. Intensions are now understood to be just what extension some words have with respect to different possible worlds. In this new usage, “water” and “H2O” have the same intension, even though their meanings may still differ. Meanings can be “finer grained” than intensions.
I put this explanation here more for later reference, than in the expectation that you’ll understand what it’s saying the first time you read this. These issues about water, H2O, different possible worlds, and so on, are ones we’ll introduce and explore more later in the semester.
Another way that intensional gets used is to characterize certain ways of talking. We said that if Lois kicks Clark Kent, and unbeknownst to everyone, Clark Kent is really the same person as Superman, then she’s kicked Superman too. Also you can’t kick someone who doesn’t exist. Most verbs and other words that need arguments work like “kicked.” On the other hand, you can fear Superman, without its being obvious that you also fear Clark Kent. Or you can fear ponies, without ever having met and feared a specific pony. Or you can fear trolls, even if trolls don’t really exist. So verbs like “fear” seem to be different. Words that work like “kicked” are called “extensional”; and words that work like “fear” are called “intensional.” The latter kind of behavior seems to be exhibited both by talk about propositional attitudes, and by talk about intentional objects (if that’s different). It may be exhibited by other kinds of talk too; that’s controversial. (For example, talk about explanations.)
The cases where Leibniz’s Law can’t validly be applied — cases that have to do with what people think, or have evidence for believing, or doubt, and so on — cases that seem to essentially involve people’s perspective on things — those are cases philosophers label as using “intensional language.”
This is related to the use mentioned above, in that extensional language depends only on the extensions of the words used (and how they’re put together — “Lois kicked Clark” says something different than “Clark kicked Lois”), whereas intensional language depends on more specific aspects of the words’ meanings/intensions.
The word “intentional” on the other hand (with a “t”) is mostly used in philosophy in one of three ways:
In his Philosophy of Mind textbook, Kim uses the label “content intentionality” to talk about whatever is going on with mental states that have propositional content. He uses the label “referential intentionality” to talk about intentional objects.
Those two options are most common in the philosophy of mind, and they’re definitely using “intentional” as a bit of special technical jargon. The third use is more common when discussing actions and related issues (practical reasons, free will); and it uses “intentional” in a way that’s closer to its everyday English meaning. In this sense, to call something “intentional” means:
For example, if you’re gloating to me about having grabbed the last beer at the party, and then I “accidentally” trip and bump you, making you spill the beer, then we might get into an argument about whether I bumped you intentionally. When people talk about your “forming an intention” and your “doing something intentionally,” they’re talking about your actions and decisions and motives in this way.
In philosophy of mind, though, I think you’ll most often see “intentional” used in the first way. Try replacing it with “propositional” or “representational” and see whether what the author is saying still makes sense. (Intentional states in this sense include, but are not limited to, decisions and intentions in the third sense.)