We can use this sentence "I never knew you liked dogs" .
But I dont get it why do not we use " I never knew you like dogs " instead of the first sentence.
We can use this sentence "I never knew you liked dogs" .
But I dont get it why do not we use " I never knew you like dogs " instead of the first sentence.
Expressions like I never knew, I never thought, I never suspected are all constructed in the past tense even though the speaker generally goes on to describe their implications for the present. In such constructions, the verb in the subordinate clause is expressed in the past tense in what's known as backshifting.
To say I never knew is another way of saying I didn't know but with more emphasis, as if to express some surprise at the turn of events.
So if you were really surprised to find someone who avoided dogs showing affection to your dog, you might well say:
I never knew (that) you liked dogs.
rather than just I didn't know...
Because the main verb knew is in the past tense, you backshift the verb in the subordinate clause from the present tense to the past, even though it still holds true.
Note that didn't know can be followed either by like or liked. As is frequently the case, here backshifting is optional.
You will find numerous explanations of backshifting online, including at:
https://thegrammarexchange.infopop.cc/topic/backshift-and-reporting-verbs
https://www.thoughtco.com/backshift-sequence-of-tense-rule-in-grammar-1689017
Confusion about "Backshift" of Verbs in Indirect Speech (To Kill a Mockingbird)
Because you need to backshift - if the main clause is in the past tense, the subordinate clause almost always needs to be in the past tense too (with a few exceptions).
A: I like dogs! I thought I told you that I liked dogs.
B: Nope, you never did. I didn't know you liked dogs. Now I know that you like dogs.