The title of of this page is a bit of a “bait and switch,” because my advice about trying to sound smart in your writing is very simple: Don’t.
Trying to sound smart almost always backfires and results in the exact opposite. Or, to put it more gently, the best way to sound smart is to try to be as clear, concrete, and direct as possible. When you make clear statements and the reader understands exactly what you mean, the reader will view you as smart and educated. On the other hand, if you go out of your way to use abstractions or “big words” to sound smart, you will usually just confuse the reader. And the confused reader will not think “Wow, this writer is so smart.” They will think “Wow, this person doesn’t know how to write clearly.” For example, contrast these sentences:
(1) Writing is difficult, but it gets easier with practice.
(2) The process of textual production is onerous, yet it becomes perfunctory as a result of successively repeated efforts.
These sentences mean essentially the same thing, but the first one is clear and makes sense, while the second one is unnecessarily difficult to read. If someone were to write the second one in an email to me, for example, I wouldn’t be impressed by the author’s vocabulary. I’d be dumbfounded that the author uses so many words to say so little.
Also, unnecessary abstraction can make things confusing. Contrast these two sentences:
(a) The bully punched the small kid in the arm.
(b) The bully behaved aggressively toward the small kid.
When I read (a), I know exactly what happened. When I read (b), I don’t. It’s not that (b) is grammatically incorrect. It’s not even that (b) is unnecessarily verbose, like (2) above. It’s just that (b) is kind of vague and abstract. What exactly does “behaved aggressively” mean? “Behaved aggressively” could mean a whole range of abusive behaviors, including yelling, insulting, threatening, throwing things… you get the picture. If I want to say that the bully hit the small kid in the arm, I should just say that directly. Being direct doesn’t make my writing sound “stupid” or unintelligent. Quite the opposite. It makes my writing seem no-nonsense and on-topic. Those are good qualities. See this post on abstraction and vagueness from the Thesis Whisperer for more on this point.
Now, does this mean that you should never use abstractions? Does it mean that you have to deliberately “dumb down” your writing to make it accessible? No. If you are talking about an abstract concept, abstract terms are necessary. For example, if I was writing a philosophy paper on the nature of “freedom,” that’s an abstract concept. You can’t pick up freedom or buy it at the store. So, of course you’ll have to use abstract terms to talk about it. Or consider mathematics: the number three (or any other number, for that matter) is an abstraction—you can’t go visit the number three, or capture it in a net, or observe it in the wild. So, if we were discussing philosophical concepts in math, we would need to speak in abstractions.
However, it’s best to use abstract terms when discussing abstract things, and concrete terms when discussing concrete, definite things.
The same goes for technical terms or “jargon.” Sometimes these are necessary. But if a particular term might not be familiar to your reader, you should define it. For more info on this topic, and related ones, see my Style and Clarity page.
Note: Another version of the text on this page appears on my FAQ on Admissions Essays page. In other words, this advice is relevant to academic writing in general, which includes both admissions essays and research writing.