Should and Ought, Must and Should

http://www.perfectyourenglish.com/grammar/should-ought-must.htm

The Romans use the same word for "must" and "should".

"Debeo" is the Latin word for "I should" and "I must".

http://www.classicsunveiled.com/romevd/html/vocabd.html

We should of course do the things we must.

We must then do the things we should.

"Should" could mean "likely to happen, all things being equal". It also means "the proposal being discussed *is* the correct moral action to take".

But only the wise know both whether something is going to happen and whether it is morally satisfactory.