I'm discussing internals of a database system with someone and I'm struggling to figure out how do I talk about my past thought on the subject.

If I was just expressing my thoughts I would say "It is the visibility map that controls whether we do a heap fetch, and the map bits are set only by vacuum".

However, I need to express my past thoughts about it, which might be incorrect. My gut feeling suggests to say "I thought it was the visibility map that controls/controlled whether we do a heap fetch, and its bits were set only by vacuum". But I'm not sure about controls vs controlled and I feel like I need a general rule for this kind of situations.

Upd: regarding whether I don't think this any more: originally my sentence was something like "I thought ..., was I wrong?" or "I thought ..., but now I'm less sure."

  • If you use "I thought", this implies that you no longer think this way - you have changed your mind. Please can you explain a little more about what you are trying to communicate. The tense will depend on that rather than simply considering the time when things happened. – chasly from UK Mar 18 '19 at 10:24

Regarding the specific question, whether to use past or present tense in this context my advice is, relax! Past tense is probably more correct, but native English speakers might use either. The point is, that use of one or the other does not change the meaning of what you are expressing, or the ease of understanding it. As chasly notes, there is some implication that you have actually changed your mind, when you use "I thought" in this way. That can be softened by adding an explanatory "...but now I am less sure..." or something to that effect.


This is a question that native speakers probably don't even think about and end up doing either way. That said, allow me to do this the lazy way and refer you to a helpful section in www.englishgrammar.org:


Basically, in this case you'd use the past tense ALL THE TIME, but if you were thinking about a general truth (something that is always true), you CAN use the present tense to talk about those truths, like this:

I thought it was the visibility map that controls whether we do a heap fetch, and that its bits are set only by vacuum.

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