While most synonyms differ from one another in nuance and contextual meaning, which users of a language may easily discern, perfect synonyms do not differ at all. Content, gleeful, cheery, jovial, and euphoric are all synonyms of happy, yet a speaker comfortable with our language can tell that they are not all identical. Some synonyms, like content, might be close in meaning and possibly interchangeable in many contexts, while others, like euphoric, have a specific connotation and do not work in most situations. This nuanced difference—be it tone, situation, formality, connotation—gives most synonyms their value.
Perfect synonyms lack such value. One of the perfect synonyms should almost always be preferred, whether it is briefer, clearer, more common, or simpler to use. For example, use and utilize are perfect synonyms, and the latter can be done without in all modern English—it is a lengthier redundancy that serves no purpose that use can’t handle better (see use or utilize). Some perfect synonyms, such as flammable and inflammable, may also lead to confusion (see flammable or inflammable), which again leads to one of the words acting as the superior option. Fortunately, few perfect synonyms exist in our language, but be wary of prolix corporate jargon that shifts verbs to nouns (e.g., ask in place of question) and nouns to verbs, which tends to be a common modern source of perfect synonyms and other sloppy usage. Be also wary of the writer who seeks longer, often Latinate words over their simpler, often Anglo alternatives.