I’ve waited to discuss the most important of our modal auxiliaries, the word that is the past tense of will, and also therefore the marker for our conditional tenses: would.
We call ’em conditional because they hold true only if certain conditions are met. Typically, we have a contrary-to-fact statement in one clause (which grammarians used to call the protasis) and the conditional in the next (which grammarians used to call the apodosis):
“Mr. Priscian,” said the doctor, “I’m afraid you are suffering from a compressed apodosis, just between the neck and the spine.”
“Oh dear, I knew I shouldn’t have gone cliff jumping! But can’t you stretch it out again?”
“Well, Mr. Priscian, if we knew how to do that, we would give you a couple of turns on the rack and send you straight home with some pills. As it is, the best we can do is alleviate the symptoms.”
“And that’s your best protasis?”
“Had I a better one, I’d certainly tell you.”
For a contrary-to-fact statement set in the past, we use the double-past (past perfect, pluperfect) in one clause (in the subjunctive mood), and the conditional perfect in the other:
If I had known what I know now, I would never have trusted Mr. Capone with my life’s savings.
Very often we use the conditional when the conditions themselves are implicit and unexpressed:
I wouldn’t do that (if I were you).
I wouldn’t do that (if you paid me a million dollars).
I wouldn’t do that (under any imaginable conditions).
I wouldn’t do that (for love or money).
I wouldn’t do that (unless you promised me you wouldn’t tell: that is, if you did not promise me that you would not tell under any imaginable conditions).
Sometimes would is used as the past subjunctive of will, to express a present wish:
“What would you like, sir?”
Would that I had that villain in my grasp!
Would you be seated?
The funny thing about would: the silent l does belong there: Middle English wolde (German wollte). But it does not belong incould. It snuck into that word by analogy with would and should. It should be coud, and would have been, but who coud be bothered about it during the Hundred Years’ War?