If you write "If I was president, I'd...", you're in error. You should write "If I were president, I'd..." The same rule applies to several situations. This is the subjunctive tense. If you want to be respected by the merit of your writing, use it.
I'm not all that great in figuring out English grammar. I know my Greek far better, so it's difficult for me to piece through this (I was arguing with my mother the other day about how it might just be possible to use anything other than a possessive after a gerund, but I was apparently proven wrong.) However, I'll comment as I can.
In Greek, subjunctive denotes, primarally, an admonition, something like 'let us do this.' Deliberations are also encompassed by this, I think. Okay, here we go. Found the page in my text. It's either an exhortation, a deliberation, a prohibition, or an expression of purpose (ie. 'so that such and such').
Lines like 'I would' or 'I should' or 'I may' fall under a different mood, which is the optative. 'I would go' would be expressed in the word Bainoimi (whereas simply 'I go' is baino, and 'I will go' besomai). The 'oi' there pegs it as an optative. It follows a totally different set of endings (or at least additions) which tend to indicate things that express a wish, or even the word could.
Now, there is a further trickiness that is difficult to express in English, and that's aspect. They have a few past tenses, but particular is the aorist. This denotes a single or short action. Now, the optative mood automatically is in the future, of sorts ('I wish that this had happened' is an indirect statement.) As such, using a present, or past aorist, has profound implications not in tense, but in aspect, or the length of the action. If wish is in the aorist optative, it is wishing for a quick action (ie. 'may you help me quickly'); in the present optative, a long one ('can you be there for me') That's Greek.
As I've already said, I'm not up on the exact rules of grammar in English. I write by what feels right, but I'm sure that often leads me astay. Just going to my Greek text (we just looked at conditionals, and an 'If/then' is a conditional sentence') ... yeah, I suppose you're right. Though this is just one of those circumstances where my gut would mislead me. I'd probably have put 'was'. That, however, on second thought, is merely the simple past. What you'd be saying is 'If I was at one point in the past president, then I'd...' but of course that doesn't follow. WHEN I was. That works. If I AM. That too works, though that is a Present Particular. I suppose in English, when expressing what would have been the outcome of something that never was, we must use the subjunctive, though admittedly I'm not familiar with it in English (save by what little comes naturally). Interestingly, however, it strikes me that what we call the subjunctive in English might often be optative in Greek. 'Were I a writer!' It is an expression of a wish. That is optative. 'Let me be a writer'. That is subjunctive. But we don't have an optative in English... do we? I suppose it's all subjunctive. Everything imaginary, whether through hope or will, that is not definite to happen, becomes subjunctive, whereas in Greek it is further subdivided. Sorry for continually referring back to Greek, but I honestly know the rules of its grammar, or at least the technicalities, better than English, and often I'll compare the English to the Greek, rather than vice versa.
Back to the thing at hand... considering it a bit more... 'If I was president' works, but it means something different. It's like saying 'I write good'. Well, you can say it. But the 'good' does not describe the verb, of course, but that the result is in a state of 'good' (like saying 'I do good' as opposed to 'I do well'... both are acceptable, but they mean different things.) Likewise here. You can say 'if I was president', but people will begin questioning your memory. Oh, but of course you couldn't construct the second part with an 'I'd', either. You'd need a 'was', or something like that. Interesting. Is that the only subjunctive we possess? In Greek, ever verb can be turned into a subjuctive, or optative. But in English, I can't see any verb being a subjunctive. How do you express desire to run? 'I wish I were running'. Running becomes a participle, but there's that helper subjuctive there. I guess we don't exactly have much of a future tense, either. We just use 'will'. So what DO we have then? Present and simple past?! I had been running... nope, again 'to be' plays its part. Wow. I hadn't quite considered that. But people can look at it this way. Take off the 'if' from the conditional. It becomes more of an exclamation. 'Were I president...' but you can't say 'Was I president...' I guess that's the easiest way of proving it to oneself.
Anyway, long story short, good point ZeaLitY. I'll try and remember that, seeing as that seems to be something I'd be prone to overlook. Something easy to miss, if one's not trained well in it. I guess we should all remember: 'was' only for past tense; if you wish to express a wish, or anything that has not, or may not, materialise, use 'were'. Right?
