Pter

“rank the degree of certainty in these statements”

1. It may take a few months to complete.  [It is possible that it will take ...; the speaker is being non-commital]

2. It could take a few months to complete.  [It is possible that it will take ... under some hypothetical condition(s) perhaps; the speaker is hinting that problems may arise which will prevent earlier completion; also non-commital.]

3. It would take a few months to complete.  [under some unstated or implicit condition(s), in an imaginary, hypothetical situation]

4. It should take a few months to complete. [It is expected that it will take ...; the speaker is estimating based on his knowledge of similar situations.]

5. It will take a few months to complete.  [confident assertion; the speaker claims to know]

As listed, 1, 4, and 5 are more or less in order of ascending optimism.  2 hints at problems (to my ear), so it might be considered even less optimistic than 1.  3 seems to require more context involving the conditions.  Otherwise 3 is just a more tentative version of 5.

CJ 

CalifJim

“Language is not mathematics.  Your approach is completely wrong in my opinion, even though certainty does figure into some of these expressions, particularly the last.”

1. I am non-commital;

2. I am just making a general statement.  The complexity of different problems varies to a large extent.  Some unexpected situations may arise (and often arise) that will prevent earlier completion;

3. The completion date is conditional on availability of certain resources. 

So, I got a match for all 1, 2 and 3!

Perhaps, I should re-word the question in terms of degree of commitment.

CalifJim

“It seems to be that the problem you're facing is not a grammar problem, but an interpersonal communications problem!  It seems that you're bargaining.  Set your time high and see what kind of reaction you get! ”

Does it mean MAY carries the meaning that the situation is under my control, but I just don't want to commit.  I can do it faster or I can do it slower.  It's just up to me. If so, this is not the meaning that I want to convey.  I'd better choose 2 then.  Do you think so?

Does it mean MAY may carry the meaning that the situation is under my control, but I just don't want to commit?

I know MAY just suggests that an outcome is possible.  Maybe I'm pushing it too far.  What I actually meant is that would someone interpret my statement as "you just don't want to commit".  And to avoid the chance of being interpreted this way, should I better use option 2?

I forgot one more option:

It might take a few months to complete.

To me, may, might, would, could, all carries a certain degree of uncertainty.  Sometimes, I really find it difficult to choose the right (best) word for the right situation.