Use so and very with caution.
Long-time listeners may remember that the issue of very as an intensifier came up when I talked about modifying absolutes. Most people believe that very is out of place and not the best choice in phrases such as very unique and very dead, where it modifies something that doesn't have degrees. You’re either dead or you're not. Very dead isn’t more dead than just plain old dead.
Still, very shouldn't be banished from the language. Merriam-Webster's Dictionary of English Usage notes that E.B. White used the repetition of very to excellent effect in a letter, writing, "It was a day of very white clouds, very blue skies, and very dark green spruces." White is the co-author of the famous style guide known as Strunk & White and formally titled The Elements of Style, and I agree that the effect would be lost if White had written, "It was a day of snowy clouds, oceanic skies, and evergreen spruces."
In addition, the Chicago Manual of Style includes phrases very long titles, very wide tables, very small numbers, and so on. It would seem silly if they instead talked about something more creative like lengthy titles, expansive tables, and itty-bitty numbers. Very long, very wide, and very small get the point across more clearly (although Chicago could probably also get away with just long, wide, and small) (6, 7, 8).
Finally, I shouldn't have to tell you this, but just to be safe, very is spelled v-e-r-y. Vary with an A (v-a-r-y) is a verb that means "to differ or change."
Don't use the word so by itself as an intensifier in formal writing, and be careful when you use the word very. It's usually better to use a stronger adjective to describe something than to throw a so or a very in front of a weak adjective. You can use very as an intensifier when it creates a nice effect or is the clearest choice, but make sure you aren't dropping it in just because you're being lazy.
1. Brians, P. Common Errors in English Usage. Wilsonville: William, James & Co., 2003, p. 192.
2. “So.” Merriam-Webster’s Dictionary of English Usage. Springfield: Merriam-Webster, 1994, p. 855.
3. Dictionary.com. Dictionary.com Unabridged (v 1.1). Random House, Inc., http://dictionary.reference.com/browse/so (accessed October 18, 2007).
4. Lynch, J. "Wasted Words," Lynch Guide to Grammar, http://andromeda.rutgers.edu/~jlynch/Writing/w.html#wasted (accessed December 16, 2015).
5. Garner, B. “Very.” Garner's Modern American Usage, 3rd edition. Oxford: Oxford University Press. 2009, p. 842.
6. “Older titles and very long titles," The Chicago Manual of Style, 16th edition. Chicago: The University of Chicago Press, 2010, section 14.106. http://www.chicagomanualofstyle.org (accessed December 16, 2015).
7. “Adjusting and checking tables," The Chicago Manual of Style, 16th edition. Chicago: The University of Chicago Press, 2010, section 3.84. http://www.chicagomanualofstyle.org (accessed December 16, 2015).
8. “Powers of ten," The Chicago Manual of Style, 16th edition. Chicago: The University of Chicago Press, 2010, section 9.9. http://www.chicagomanualofstyle.org (accessed December 16, 2015).
Note: This is an update of an article that originally ran October 19, 2007.