Pancakes can be made on a stove.

They could have been made in the oven, but they wouldn't have turned out so good.

(possibility)

Bikes may be ridden on this bike path.

Earlier, these bikes might have been ridden through the streets of Minneapolis.

(permission is given)

Flowers will be grown in my garden again this summer.

Corn would have been grown last summer, but corn stalks take up too much space.

Her work has to be done by tomorrow or she'll get in trouble with her boss.

It had to have been done by yesterday, but her boss gave her extra time to finish it.

Something should be done about global warming or else some types of penguins will perish from the earth.

Something should have been done many years ago but wasn't.

A lot of cows can be raised on a productive farm.

Corn could have been raised instead, but this farmer decided to grow grass. Smart man!