"If I was a hopeless cad, I would apologize."
This means that there is a possibility, which I am not yet quite prepared to admit, that I was a perfect cad sometime in the past. I would apologise, but what are we waiting for? We now need to know on what condition, as you have not said "I shall/will apologise, but "would apologise", so you need to go on, saying "if ..." as perhaps "if you were to convince me (that I was a perfect cad).
Complete sentence then:
"If I was a perfect cad, I would apologise if you were to convince me that I was."
This means you don'y think you will be convinced. If you think you will be, then
"If I was a perfect cad I shall apologise if you convince me that I was."

But you don't mean either of these, do you?

"If I was the Prime Minister, I would change the law." This to me suggests that I am surprised and doubtful to hear that I was sometime in the past the Prime Minister, find it hard perhaps to believe that such an thing could have been allowed, and if it is true, would want someone to change the law, maybe to prevent such a calamity in the future.
(I have, of course, by the way, no particular prime minister in recent history in mind.)
"If I were the Prime Minister, ..." has a totally different meaning, that I want the law changed and if I could I would, but I can't so I shan't because I am in fact not the Prime Minister.
Which one do you mean?

'Think to ..." is wrong, no doubt about it. It is dialect, not standard English. As an English resident for some decades I have not even heard it used. They do have some strange variations on standard English, colloquially, but not this one!
My first encounter with strange idiom in England was hearing a teacher tell his class to "stay sat", thirty years ago, and now it is quite common to hear "We were sat (somewhere) ...". Most regional and other dialect is fun and entertaining, but this one is plain ugly, and so is "think to"!

Enjoyed greatly the notion that "o'clock" is from the German. "acht Uhr" means "eight o'clock". Moved into English in stages, see the movie "Casablanca" with Humph and Lauren. Some elderly German emigrants heading for the USA are practising their English: he asks her "What watch is it?", she replies "Eight watch" and he looks surprised and says "Such watch?".
I don't think they found "o'clock" came too naturally.

Thank you all for giving me the best laughs for years, reading your stuff on all this. I see the Civil War is still being fought on the linguistic front in the good old US of A.
On the other side of the herring pond the English have a problem similar to the idea/ideal thing: peninsula (noun)/ peninsular (adjective), so 'Peninsular War' seems okay if we are describing which war, but "the South-West Peninsular" is wrong! It is the South-West Peninsula! Like your correspondents, I feel really frustrated that I can't tell people who get it wrong, and just have to seethe. I used to put them right on everything when they were my kids, but now I am retired they aren't and I just have to put up with it.
You also prove my thing about Americans using the word "that" when "who" is the right one. Or is it just a Southern thing? That is fine for Americans, and none of my business, really, but now it is happening here in the UK and I don't like it here! My rants on this matter appear elsewhere in this forum.
Please keep up the good work on idea/ideal.

If I was ... I would ... has one indicative verb (was: factual, perhaps) and one subjunctive (were: non-factual, I shall not apologise...) so the simple rule of sequence of tenses: both clauses need to be subjunctive for a closed or non-factual, or both need to be indicative for an open condition, one which may still be fulfilled. When you say "If I was ...I would, it begs another subordinate clause: "If I was ..., I would ...if ...).

This is the same problem as yesterday's one from Mr Tony Blair, former prime minister of Britain, who is quoted as saying "If I was interested in money, I could make much more", which begs the question, in more than one way, leaving us wondering how he could make much more, and when it might have been that he was interested in money, and why not any more. But he is acknowledged as a great orator who does not need any verbs in his sentences, and indeed does not always use them at all, and speaks in the dialect of his intended listeners, which is not necessarily standard English, so we must not use him as a model.

Good one, "I wish I were .....". Now, why is it "I thought I was ...." but "I wish I were ...". One is for fact, the other for non-fact. (Or "counterfactual" to cite a contributor.)+
Students of English as a second language are keen to learn these details, others treat them as an affront. Shame on the others, I say!

"I think I am..." v "I wish I were ...", This time the verb in the main clause (wish/think) are in the present tense. - uh, this time the explanation is harder: both think/wish introduce maybe yes or no subordinate clauses. So why not "I wish I am" or "I think I were"? Even more clearly, here the wishing suggests doubt (subjunctive 'I were') and the thinking suggests certainty (indicative 'I am').

Not so hard after all, hey?

Good one, "I wish I were .....". Now, why is it "I thought I was ...." but "I wish I were ...". One is for fact, the other for non-fact. (Or "counterfactual" to cite a contributor.)+
Students of English as a second language are keen to learn these details, others treat them as an affront. Shame on the others, I say!

Good one, "I wish I were .....". Now, why is it "I thought I was ...." but "I wish I were ...". One is for fact, the other for non-fact. (Or "counterfactual" to cite a contributor.)+
Students of English as a second language are keen to learn these details, others treat them as an affront. Shame on the others, I say!

OK, I found idiolect on Google dictionary, and its definition shows that "my idiolect" means that you personally choose to say "If I was ..." for 'counterfactual'. That does not mean you should.

I still maintain that to say "If I was the prime minister" means you can't remember if you were, or don't want to own up to it. To say "If I was there" allows the possibility that you were indeed there.