Does I could not do X have the same meaning as I would not be able to do X?

It seems to me that the first can mean the second, but it mainly means: I tried and I was not able to do X. Is that so?

  • Please retag appropriately! Apr 13 '14 at 19:24
  • 3
    Yes; I could not do X is ambiguous; it can mean 'I was not able to do X', 'I find doing X morally repugnant', and 'Under those circumstances, doing X would be impossible for me'. _I would not be able to do X can mean only the last two. Apr 13 '14 at 20:38

John Lawler is on the right track. The difference between could and would draws on the difference between their present formations (“can” and “will”, respectively).

“Can” simply implies physical (or other existential) ability to complete some task.

“Will” implies that the task will actually be completed (whether or not by choice).


“Could” only implies that the task was existentially possible to complete.

“Would” implies that some particular condition enabled or hindered the task from completion.

So, the “tl:dr” is, “If you intend to qualify the statement with what restrained or enabled an action, use ‘would’”.


I could not go to the market.

I would not go to the market if I already had food.

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