Terms are words or phrases that designate classes.
Singular terms designate individuals, e.g., proper nouns (“The Taj Mahal”), or proper names (“Princess Diana”).
The connotation of a term is the list of membership conditions for the denotation. Philosophical synonyms for “connotation” are “sense,” “intension,” and “real definition.” Note this sense of “connotation” differs from the literary sense.
The denotation of the general term “square” is all squares.
Few concepts are closed. Most concepts are open. This is not a big deal.
An open concept is one for which the connotation cannot be precisely specified; rather, we recognize members of the class by their resemblance to paradigms of the concept.
NOTE: When we say that the concept “disabled person” is open, we mean simply that it is hard to decide in some cases whether that concept should be applied to an individual person. We do NOT mean to say that the concept is useless. Just because it’s hard to say in some cases doesn’t mean there’s no such thing as a disabled person! Arguing that way would be committing the continuum fallacy (see below).
All the interesting social, legal, and philosophical notions are open, and require argument by analogy to decide borderline cases: “person,” “good,” “religion,” “rich,” “sexual harassment,” “obscenity,” “minority,” etc. Such argument is important because it matters what we call things.
It’s important to realize that open concepts are normal and useful, even if we can’t define them as precisely as we can define closed concepts. It IS important to define terms when we argue. But sometimes we have to settle disputes about paradigms before we can begin to argue specific cases.
Clearly, you and your opponent are using very different definitions of “disability” – different paradigms. You’re not going to get anywhere if you don’t first come to some agreement about the paradigm cases. That’s where it’s important to “define your terms.” What does your opponent think “disabled” means? The burden of proof is on your opponent in this case to argue for his notion of disability. He must show first that it makes sense (is any conscious person disabled, on his view? if no one counts as disabled, does the term “disabled” mean anything anymore?).
People are of course free to use words any way they like. But in contexts where argument matters – in the university, in science, and in public life – people must defend their eccentric word usage with arguments. In other words, people must give good reasons.