Use so and very with caution.
Today's topic is something I am very guilty of doing myself, and I’m so excited to give you the rundown: It’s overusing the words so and very.
A listener named Taryn wrote in asking if it is acceptable to write that she is "sooooooo" happy that she is going to the prom, which got me thinking about not only the word so but also the word very.
Both words are often used as intensifiers, meaning they allow you to express that you are happier than just happy.
In the formal writing world, both words are looked down upon, but so (by itself) is sometimes considered worse than very (1).
When you're speaking, emphasizing the word so seems to add punch to a simple statement—I'm sooooo happy—and this is why Taryn is tempted to write the word with so many O's: She's used to saying that she's "soooooo" happy, which is fine in informal conversation. But style guides say it should be avoided in writing. There's even a strange discussion in Merriam-Webster’s Dictionary of English Usage about whether using so for emphasis is a distinctly female failing, with the Dictionary concluding that it's a universal error even though other commentators link it specifically to women (2).
On the other hand, when so is paired with that, it becomes more acceptable in writing. For example, even though it's considered bad form to write, "I was so happy," it's OK to write, "I was so happy that I jumped for joy." When you say you are so happy that you jumped for joy, so becomes an indefinite adverb of degree instead of a vague intensifier. In other words, so leads into a thought about how happy you were.
How happy were you?
So happy that you jumped for joy.
The grammar mavens find it much more acceptable when so is linked to another clause in that way (2, 3).
Unlike with the word so, it's not considered an actual error to use the word very by itself for emphasis. Nevertheless, most style guides warn against overdoing it. Instead of saying, "I was very hungry," they encourage you to search for a single more creative adjective--something like "I was famished," or "I was ravenous." Replacing two simple words like very hungry with one more descriptive word like ravenous makes your writing tighter and usually more interesting, too (4, 5).