Do is a two letter-word, but is that a sufficienct reason not to capitalize it when using title case? The answer is no; do must be capitalized in titles since it’s a verb. Only conjunctions (and, but, or, …), (short) prepositions (at, for, in, …) and articles (a, an, the) are lowercased in title case. Verbs however are always capitalized, no matter how short they are.
Here are a few example titles that show the correct capitalization of do:
This Is How We Do It
Who Do You Think You Are?
Anything You Can Do (I Can Do Better)
Try out the Title Case Converter, which will help you capitalize your titles or headings correctly.
Photo: Millo Lin