Is the Phrase "Might Could" a Grammatical Error?

As a professional writer, I tend to be relatively strict about my daily use of language. Although I was born, bred and raised in Alabama, I generally avoid any linguistic errors that might label me a Southerner. Nevertheless, colloquial sentence structures sometimes infiltrate my daily conversations. When I'm not careful, I may find myself using stereotypically Southern expressions such as "fixin' to go" and-- as I said last week-- "I might could do that."

When a friend pointed out my use of "might could"-- a phrase that I had used many times without a second thought-- I found myself wondering if it was actually gramatically incorrect. I could not think of any specific reason to avoid the phrase, or similar phrases such as "might've used to" and "used to could."

I was relieved to find that the expression, while unconventional in most parts of the U.S., is not actually grammatically incorrect. According to the The Maven's Word of the Day, "[M]ore educated Southerners tend to avoid this construction, but that's due to a prejudice of perception, not to any inherent inferiority of the use."

Maven's Word of the Day classifies "might could" as a grammatical double modal. Other examples of double modals include the phrases "might would" and "had oughta." Because the phrase "might could" generally occurs in spoken grammar rather than written language, most people assume that it is grammatically incorrect. However, there are no formal rules banning the use of double modals, even in professional written language.

Fascinatingly, "might could" grammar persists in the South because of historic influences. Outside of the United States, it is common for people in Northern England and Scotland to use the phrase. Many Southern Americans claim some degree of Scottish or Northern-English ancestry, and the regional grammar patterns may have persisted because of these influences.

Although I may get a few strange looks from Yankees, I'll continue to say "might could" without bothering to correct myself. It is assumption, not reality, that makes the phrase seem incorrect. Now that I know that there's no harm in the phrase, I might could even get away with using it in writing.