Jane: … I want to improve my biology, what can you suggest?
Zhou lan: Well, have you considered using the lab in your free class? I suggest you ask Mr. Wu.
Jane: Well, yes, [color=blue]I could do that. But I don’t want to do anything alone.
Zhou lan: I’ve got an idea. Why not do a tomato experiment? You don’t need anything special. Ask Mr Wu if you can have some old boxes. Use the lab and prepare some plant food for young tomatoes. I mean power that… measure them (the plants) with a ruler and write down your results.
Jane: Why don’t you do the experiment? I’m sure you would do it really well.
Zhou lan: Ok. I’ve got a better idea. Why don’t we do it together?
What does [color=blue]I could do that mean here?
Many many thanks in advance.
It is the usual conditional meaning:[i] it is possible for me to do that if….
Thank you, Mister Micawber.
But why shouldn’t we use “I can do that” here? what’s the difference between the two usages?
No one said you shouldn’t use ‘can’ here, but the speaker doesn’t want to ask Mr Wu. ‘Could’ is simply more tentative.
I’ve heard from someone that it is more formal when we use “could” instead of “can” in present context (not in past context, which is easily understood). So is it right?
By the way, can we use “and”, “but” or “so” to begin a sentence? I think it may make the sentence dangling (according to grammatical rule), but I have seen this usage in many native document…
As has been explained, ‘could’ is in a way more cautious in implication. There is a difference between: Can you lend me some money? and 'Could you lend me some money? The first is more direct, the second has the underling hint of 'if that’s at all possibler in any way.
Starting a sentence with a conjunction such as ‘and’ and ‘but’ is frowned upon by some of the old fashioned grammarians but it is quite illogical and to my mind perfectly acceptable. Incidentally the construction after ‘make’ in the sense of ‘cause’ ‘force’ is the infinitive so you would say: ‘make the sentence dangle’.
I agree with Alan wholeheartedly here. The problem is that it only works in certain situations (often as a means of creating emphasis), and many learners have a penchant for inappropriately splitting clauses. That is why I caution learners against doing it.