He Walks To Work Every Day But Not ______ Thursdays.

Prepositions with Days of the Week in English

A common gap that shows up in tests and everyday writing is the preposition that goes before days. The answer to the sentence "he walks to work every day but not ______ thursdays" is simply "on." So it reads: "He walks to work every day but not on Thursdays." That is it. Nothing tricky about it. I remember grading a stack of business emails from a client team where the same mistake kept appearing. People wrote "not thursdays" instead of "not on thursdays." The sentence looked wrong, but they could not say why. They treated "on thursdays" as optional filler. It is not optional. It is part of the grammatical structure. In English, when you refer to a specific day or recurring days, you need the preposition "on." The blank in that sentence is asking you to supply it. Here is how to think about it without overcomplicating the rule. You use "on" with days of the week. On Monday. On Tuesdays. On Christmas Day. You also use "on" with specific dates. On July 4th. On my birthday. That is the pattern. It is not optional when you are talking about a particular day.

But there is a corner case that trips people up regularly. When you add words like "every," "last," "next," or "this" before the day, you drop the preposition entirely. You say "I see him every thursday," not "on every thursday." You say "she called last monday," not "on last monday." Same thing with "next friday" and "this wednesday." This is where I lost points on my own early writing, because my Portuguese background pushed me to insert a preposition where English did not want one. I had to retrain that instinct. Another edge case that actually costs people money in professional writing involves time-of-day combinations. If you say "on thursday morning," the "on" stays. But if you switch to "this thursday morning," the "on" disappears. I caught this error during a contract review once. The clause read "payment due on next monday." That is wrong. It should be "payment due next monday." The reviewer who drafted it had mixed the two patterns. Fixing it took about four minutes, but it would have been embarrassing if the other side had noticed first. If you are trying to remember the rule quickly, think of the blank in "he walks to work every day but not ______ thursdays" as a slot that only accepts "on" because there is no "every," "last," or "next" modifying the day. The word "thursdays" here means "on the recurring thursday of each week." In Portuguese you might just say "na quinta-feira" or "todas as quintas-feiras," but English requires the preposition when you are not using those determiners.

Some learners think that because "on" sounds redundant when paired with "every thursday," they can drop it in other contexts too. You cannot. "On thursday" is a fixed time marker. It does not disappear unless a specific determiner takes its place. This is one of those rules that feels arbitrary until you see the pattern, and then it stops being a problem. If you want to drill this, the most useful exercise is to take sentences that already have "every," "last," or "next" and remove those words. The preposition will reappear. "I met her next tuesday" becomes "I met her on tuesday." "We talked last friday" becomes "we talked on friday." It is a mechanical swap that reveals the underlying structure. There is also a small note about capitalization. "Thursday" must be capitalized in English. That is a separate convention, but it shows up in the same kinds of mistakes. "not ______ thursdays" should become "not on thursdays" when filled in, though in proper writing it would be "not on thursdays" with the capital T. The blank is about the preposition, not the casing, but both matter in final text.