would doesn't mean
possible in the same way that
may and
might do.
would is actually more definite, more certain, than
may or
might, because if you say something
may be true, it means
maybe it's true, and maybe it's not true.
would doesn't work that way.
would is probably the most difficult word in English to explain!
You wouldn't know him. (~ My guess is that you probably don't know him. ~ I strongly doubt that you know him. ~ There is nothing that leads me to think that you know him.)
A flight to Mars would take more than a year. (In an imaginary world where flights to Mars are ordinary events, a flight to Mars takes more than a year.) [This is a different usage from the usage in the first sentence.]
The weight of insects ... would be greater than the weight of .. (In an imaginary world where we are able to make such measurements, the weight of insects ... is greater than the weight of ....) [Same usage as in the second sentence.]
He would have reached New York. (In an imaginary world where certain conditions were met, he reached New York.)
I thought you would have finished this by now. (In an imaginary world - the imaginary world created by my thoughts - you have already finished this.)
My paraphrases are only approximate. There is no real definition of would. You just need to hear it and imitate it a lot before you start to understand how to use it. A clause with would is most often accompanied by an if clause that reveals more about the imaginary world we are in by expressing a condition.
MH, thanks for the link. I have no problem feeling and understanding CJ's examples except for the first one which I need more time to pick up. As a learner, in some contexts, the right meaning of would is very clear but in some contexts, I can't tell which of the meanings is used. That's when I need some guidance and slowly I'll be able to strenghten my knowledge of would. This is one of the contexts I can't tell. My best guess is it carries the imaginary meaning but why? They have completed the canal, and when the water level rises to the level of the canal, it WILL spill over. That's what confuses me. Hope my confusion is clear to you. Thanks in advance.