We use words to express ideas. In principle, we could use any word to mean anything we like. Meaning is usage. If all the English speakers agreed to use the word “cat” to refer to goldfish, goldfish would be what the word “cat” means. While the meaning of a word is totally up to us as a linguistic community, the only way we can ever hope to communicate with each other effectively is by coming to some consensus on how a word is going to be used. Definitions typically belong to linguistic communities, not individuals. Nobody is going to stop me from defining words however I like. But people just won’t understand what I’m saying if I get too creative about what meanings I’m attaching to the words I use. What matters is that we use words in ways that provide clarity of communication, at least to the degree that it’s required for the purpose at hand.
In everyday discourse we have a fair amount of wiggle room regarding what words mean. Many words are ambiguous, that is, they have multiple meanings and can be used to express one or idea or another (to know a person isn’t really the same thing as to know that 2+2=4). Sometimes we can reliably convey something using words in ways that deviate from any of their meanings (“I just knew he’d say that!” when I didn’t really know, but maybe just had a hunch). And words are often vague in meaning (“I’m not exactly bald, not just yet”). There are various cues, some linguistic, some otherwise social, that can usually make our meaning clear enough, if not entirely clear. But we rely on the standards of our linguistic community to fix meanings in ways that are good enough to share our thoughts.
Ordinary language only gets us so far. Often thinking clearly requires that we identify a specific idea and hold it still in order to see clearly how it relates to other ideas. To do this we introduce technical definitions for words. That is, we define a word in a specific way, with the understanding that we are going to use the word in that specific way and not in other ways in a certain context. The context may be an entire branch of study. “Adaptation,” for instance, has a specific meaning in evolutionary biology. Or the context may be a single paper. It’s quite common for a philosopher to define a word in a specific way for the purpose of formulating a particular argument. The technical definition provides a way to focus on a specific idea, often carefully distinguishing it from closely related ideas, when ordinary everyday language isn’t rich enough or stable enough to do the job.
A key step in building a rich conceptual framework involves getting comfortable with technical definitions. Having a richer conceptual framework illuminates how ideas relate to each other and affords a richer understanding of thing in general. Understanding things more clearly requires tracking technical definitions and then keeping the specific idea they pick out in mind in subsequent uses of the word.
Usually, when I start to introduce students to how words are used in philosophy, they quickly get distracted with what the word means to them. This is quite literally a distraction. As soon as I start thinking about what a word means to me, I’m changing the topic from whatever idea we set out to analyze in favor of something else that’s going on in my head. This will invite confusion.
Staying on topic can be challenging in philosophy, especially since many of the ideas we are trying to analyze and better understand are among the assorted and sometimes closely related meanings of familiar words. For instance, you are familiar and competent with the word “know,” but you’ve probably never had occasion to reflect on how knowing your best friend doesn’t really get at the same idea as knowing that 2+2=4. This makes it all the more important to watch for definitional remarks and stay focused on the specific idea we want to examine. All the other ideas you might be interested in are out there and they may well be worth examining in their own right. But one project at a time. Otherwise, we wander aimlessly and lose track of what we originally set out to examine.