Can vs. Could

“I always have trouble using ‘can’ and ‘could’ in a sentence. Could you please help?”

Well, not only could I help, but I can. And I will!

The word “can” expresses power or ability.

Example
I can provide the answer to your question.
I can finish the book by Friday.

Years ago “could” was the past tense of “can.” However, it is no longer used in this sense. “Could” now implies a probability factor – usually about 50 per cent.

Example
I could provide you with an answer (But I may not).

I could finish the book by Friday. (The activity is possible but not guaranteed.)

And for the sake of politeness, we also use “could.”
Example
Could you please set the table? (more polite)
Can you please set the table? (more direct)


Conclusion: When you say “I can” you are just establishing that you have the ability to do so. When you say “I could” you establish that, yes you have the ability, but it’s only a possibility that you will go.