Reading an scientific study on germs. I say to my professor:

I wish I could understand it but I just can't.

VS

I wish I could understand it but I just couldn't.

Question

Reading an scientific study on germs.  I say to my professor:I wish I could understand it but I just can't.VSI wish I could understand it but I just couldn't.

CalifJim · Accepted Answer

bebopI wish I could understand it but I just can't.

Correct. 'wish' takes a backshifted verb, so 'can' becomes 'could'. The scope of the verb 'wish' does not extend into the second clause (beginning with 'but'), so 'can' pops up again (can't).

bebopI wish I ~~could understand~~ could have understood it but I just couldn't.

The correct version is shown in red. 'could' is backshifted to 'could have', again because of the governing verb 'wish'. Again the scope of the verb 'wish' does not extend into the second clause, so 'could' pops up again (couldn't).
____________

The first one is a wish about the present state of affairs and your hope for the future. The second is about the past, and it says that you did not understand it, though you wish otherwise.

CJ

Bebop · Answer

Perfect explanation.  Thank you so much!

Reading an scientific study on germs. I say: I wish I could understand it but I just can't. VS I wish I could understand it but I just couldn't.

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