Say it again, Sam

You start a conversation, you can't even finish it
You're talking a lot, but you're not saying anything
When I have nothing to say, my lips are sealed
Say something once, why say it again?

So go the lyrics of "Psycho Killer", one of Talking Heads' biggest hits. This verse is also a good description of tautology, and why it can be frustrating to be subjected to. For the uninitiated, tautology is a statement which repeats an idea, essentially saying the same thing again. There are points where an intentional tautology can be quite useful (you'll see me pull them out from time to time to help explain concepts, as I have done in this very paragraph), but when implemented unintentionally, as they often are, they rarely add to your text and can become grating if overdone.

Examples of tautology can pop up in all sorts of everyday language, such as phrases like "convicted felon" (you can't legally be a felon if you haven't been convicted) or "illegal trafficking" (trafficking is, by definition, illegal). This is a sort of logical redundancy, where the adjective is implied by the definition of the noun it's describing. By making a point of including the adjective anyway, a writer may be intending to emphasise that aspect of the thing they're describing, but the effect is often an implication that the thing might sometimes not align with the adjective. To illustrate, the phrase "assless chaps" implies the existence of "assed" chaps, which are better known as trousers, and "burning fire" suggests that some fires might, I don't know, freeze?

One particular type of tautology is the logical tautology, a statement which is incapable of being false. Sometimes the logic is circular (blue curtains are blue), or it encompasses every possibility (they're either blue or they're not), or it's just extremely fundamental (Marvel movies are popular because people like them). In any case, it states the obvious in a way that's generally unhelpful, because it doesn't communicate anything meaningful by the wayside.

Another common form of tautology is RAS syndrome (redundant acronym syndrome syndrome), which is a great example of what it represents. As you have probably guessed, this form of tautology is when one of the words of an initialism gets appended to the end of the initials, as in these frequently-used examples:

• PIN (personal identification number) number
• ATM (automatic teller machine) machine
• RAT (rapid antigen test) test
• HIV (human immunodeficiency virus) virus

A lot of sort-of-tautological terms come into being when words are borrowed from other languages, such as naan bread or chai tea ("naan" and "chai" are words taken from various Indian languages that mean "bread" and "tea" respectively). However, because the borrowed word becomes a descriptor for a specific type of bread or tea or whatever, the etymological tautology doesn't transfer into the meaning of the phrase. Place names also fall victim to this process, such as the many Avon Rivers crossing Britain ("Avon" being the Romans' interpretation of various local words meaning "river"), Mount Maunganui ("Maunganui" is Māori for "big mountain"), the Mississippi River ("Mississippi" is Algonquian for "big river"), and Gezira Island ("Gezira" is Egyptian Arabic for "island").

So when might a tautology be genuinely useful, and not just unnecessary or confusing redundancy? The first use case is for clarification; if a word or phrase is introduced that may not be widely understood, a simpler synonym may be added to illustrate its meaning. This is frequently seen in the context of law, where (in England, at least) the language of government was for a long time very different to the language of the people—Latin and French compared to English, respectively. For clarity, legal phrases started to include both the official Latin- or French-based term with a more vernacular English-based one, and we can still see the tradition carried through in legal terminology today, as in terms like "cease and desist", "null and void", and "will and testament".

Humour is another useful home for tautology; like malapropism, it's a literary device that lends itself easily to nonsense. Yogi Berra, for example, is well known for using both tautology and malapropism in his "Yogi-isms", amongst other techniques. You could give tautologies to a character who you want to make more ridiculous, or use an obviously self-aware tautology to lighten some prose. Alternatively, a string of tautologies could build up emphasis to a humorous level, whether you intend it or not. The character Polonius in Hamlet is an incurable tautologist to great effect, which makes his statement that "brevity is the soul of wit" deliciously ironic.

Finally, I want to mention the use of tautology in rhetorical or poetic language. Because this context is inherently heightened in comparison to plain prose, there's a higher threshold before things become silly. Phrases and ideas can be repeated in this context and it's meaningful, not redundant. In poetry and song especially, tautology might help lean into a theme and interact with structural techniques like rhyme and metre—Edgar Allan Poe's poem "The Raven" is a good example of this. In other rhetorical contexts, such as speeches, tautology can be used effectively as a form of emphasis to hammer home an important, repeated idea.

As with all literary techniques, the important thing to remember about tautology is to be thoughtful about it, to know how to identify it and discern whether it's adding to your writing. It has its place, but also has a tendency to crop up where it shouldn't. So, now that you know more about what tautology is, go and wield it with skill, competence, and capability!