Today's search:
"since when do you eat" has 89 possible results.
"since when have you eaten" has 19 possible results.
"since when did you eat" has 18 possible results.
According to tense-changing process, <Present Perfect + Since> has come from Simple Present:
1. I eat salad. (a present action)
2. I have eaten salad. (a past action)
BUT: If we mention a definite past time, we have to change the two tenses above:
3. I have eaten salad since 1987. (=1, a present action)
4. I ate salad last week. (=2, a past action)
Please note that Indefinite Time, like 'every day', doesn't start the tense-changing process:
a. I eat salad.
b. I eat salad every day.
== Indefinite Time doesn't change Simple Present to Present Perfect.
Asking "since when?" is an awkward moment.
-- Have we added a definite past time to the question?
-- Have we added an indefinite time to the question?
-- Have we mentioned any time at all?
It seems that people's opinions waver here. Obviously, <since when + Simple Present> is of most support. It means that, in asking "Since when?", most believe they add an indefinite time only, which doesn't change Simple Present to another tense: "Since when do you eat salad?"
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Some may argue that, as they are asking of the time, they don't pre-add the time to the question. At this point, they just add "since when" to a question "Did/Do you eat salad?"
"since when do you eat" has 89 possible results.
"since when have you eaten" has 19 possible results.
"since when did you eat" has 18 possible results.
According to tense-changing process, <Present Perfect + Since> has come from Simple Present:
1. I eat salad. (a present action)
2. I have eaten salad. (a past action)
BUT: If we mention a definite past time, we have to change the two tenses above:
3. I have eaten salad since 1987. (=1, a present action)
4. I ate salad last week. (=2, a past action)
Please note that Indefinite Time, like 'every day', doesn't start the tense-changing process:
a. I eat salad.
b. I eat salad every day.
== Indefinite Time doesn't change Simple Present to Present Perfect.
Asking "since when?" is an awkward moment.
-- Have we added a definite past time to the question?
-- Have we added an indefinite time to the question?
-- Have we mentioned any time at all?
It seems that people's opinions waver here. Obviously, <since when + Simple Present> is of most support. It means that, in asking "Since when?", most believe they add an indefinite time only, which doesn't change Simple Present to another tense: "Since when do you eat salad?"
-----------------
Some may argue that, as they are asking of the time, they don't pre-add the time to the question. At this point, they just add "since when" to a question "Did/Do you eat salad?"