Language is a set of tools people use to communicate with each other. There are means of face-to-face communication that do not involve spoken language, such as gesticulation and facial expressions, but language makes communication easier and more efficient. And just like with any other set of tools, the better our command of language, the more easy and efficient is the process of communication.
Human communication is a complex process even when the subject is very basic and apparently simple. When we accidentally cut a finger with a kitchen knife, we are likely to exclaim a simple sound that a family member in the next room would normally interpret as pain. But when asked “What happened?” we are immediately called to a task much more complex than a simple exclamation. We feel the need to describe what is it we were doing (“I was chopping scallions”), what happened (“and I cut my finger”), and what is going on now (“I am dripping blood all over the place”), and what can the other person do to help (“can you please bring some Band-Aids from the bathroom?”). The fact that without much apparent thought we find the correct words and put them in the correct order for the other person to understand what we mean does not make the task any less complex. But when the ideas and information we want to communicate become more complex, the task of communicating them becomes even more so, and we have to choose more carefully from our language toolbox. When reporting a kitchen accident, it doesn’t make much difference whether we were chopping the scallions, or dicing or mincing them. Neither is it material whether the vegetable in question was in fact a scallion or a shallot. But if we are asked for a recipe for a fancy French sauce, these details can make all the difference, and thus require of us to find the precise verbs and nouns to communicate the correct information.
From the above example we can see that words which are considered synonymous in one context will not be viewed as such in a different one. The language toolbox has a tool for almost any conceivable situation. Even though some tools can be used interchangeably some of the time, they are by no means exactly the same, as the phrase ‘true synonym’ seems to imply. A wrench can be a reasonable substitute for a hummer in the absence of the latter, or a pen can substitute for a pencil when erasability is not an issue. Still, these are different tools intended for use under different circumstances. We can substitute one word or phrase for another, but not all the time, and not under all circumstances.
One of the language constructions which can define a context is collocation. Fancy French sauces aside, practically speaking chopping onions is roughly the same as mincing them, which makes the two collocations interchangeable most of the time. But if we change the context and take the common collocation mincing words, the word chop will no longer be even nearly synonymous with mince.
Another consideration that affects the context in which a particular word is used is register. Mincing words can usually mean the same as not being straightforward, or beating around the bush. But these expressions belong in distinctly different registers, and so are not automatically interchangeable. At the same time, they are useful tools to have in case we do want to deliberately raise or lower the register of a sentence.
One man’s liar is another man’s diplomat. Connotation can be everything, and so mincing words or beating around the bush is not nearly the same as being diplomatic or tactful.
Finally, even the same word can mean slightly different things when used by different people or even by the same person on different occasions. Even when we are asked for a Band-Aid, we cannot be sure as to what kind or size is preferred, without being explicitly told. Words are symbols, and as such are only approximate reflections of objects and ideas. No two people, objects, thoughts or ideas are exactly alike, and so it logically follows that the same is true about words.