Can you trademark THE?
In the believe it or not category.
The Ohio State University recently filed a trademark application for the word THE as a trademark for use on "Clothing, namely, t-shirts, baseball caps and hats" (see TSDR link for application serial number 88571984).
Yes. You got that correct. They filed for a trademark application for the most common word in the English language (see Wikipedia link).
I suspect the USPTO is not likely to register this trademark because it is a standard character mark. If they had filed a design mark (logo) for the word THE, it would have increased the likelihood the USPTO would register the mark.