"I can't seem to" vs "I can't"

Solution 1:

The use of seem to is usually a hedge, or a softener. The examples above are suggesting that the person feels they should be able to do something but cannot find the right way to do it successfully. The same person wouldn't say, "I can't seem to speak Korean" because they have no reasonable expectation that they should be able to speak Korean.

Solution 2:

"I can't seem to" expresses the idea of repeatedly trying without success. You don't want to flatly admit that you can't as long as you keep trying, but you're closer to failure so it seems you can't, while you still hope to succeed. It's often used as a commentary on ongoing attempts:

I just can't seem to get this jar open!

The expression is somewhat informal.

"It seems that I can't" expresses a bit more finality. It's as if you've seen all the attempts, and while you may succeed in some future attempt, you have say at this point that it's unlikely.

Why the two expressions have these slightly different meanings is something I can't seem to figure out.

Edit:

• struck out comments on positive "seem to".
• I realize I have defined "can't seem to" in terms of "seems you can't"! Oh well.

Solution 3:

I’ve often wondered about this myself, Meysam. ‘To be unable to seem’ is a strange state to be in. Of course, what speakers who use this construction (and I am of their number) are saying is ‘It seems that I can’t . . .’ That’s what would be used in formal writing. For example, we’d expect an economist writing in a serious publication to say ‘It seems that the government is unable to control inflation.’ We wouldn’t expect ‘The government can’t seem to control inflation.’

So, yes, I think you’ve hit on the answer. ‘I can’t seem . . .’ is informal and, I suspect, widely used. How, when and why it came about would make an interesting little study for anyone with the time to pursue it.

Solution 4:

The distinction is important, particularly in psychotherapy...

"I can't" is final and definitive, as has been suggested by several answers. In other words, "I cannot and never will be able to..."

"I can't seem to" is alternatively expressed as "I can't, yet," or "I can't, at the moment." In other words, it allows for the possibility that a given thing can be achieved, which "I can't" doesn't allow.

This distinction becomes clearer if I illustrate it with a specific example... "I can't shake this depression." If one says this repeatedly to oneself, one programmes oneself to believe that it is true, and people who are suffering from depression are encouraged to add "yet" on the end of the statement. Admitting the very possibility that the thing can be achieved is often sufficient to cause a person to make it true in a person's mind.