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?

I am opening my Bible to the New Testament, at random. I read: “And he said unto his disciples, Take no thought for your life, what ye shall eat; neither for the body, what ye shall put on.” I read: “And which of you with taking thought can add to his stature one cubit?” I read: “And seek not ye what ye shall eat, or what ye shall drink.” If it is good enough for Almighty God, it had better be good enough for a dusty old English teacher.

The fact is, English stylists have always begun sentences with and. Bede the Venerable did it in the eighth century. Chaucer did it in the fourteenth. Shakespeare did it in the sixteenth. Milton did it in the seventeenth, Swift did it in the eighteenth, Twain did it in the nineteenth, and Hemingway did it in the twentieth. Every single great English writer without exception has begun sentences with and, and plenty, too. It is the easy way to connect, loosely, one sentence with another. It’s swifter than the pedantic in addition, comma, or furthermore, comma, or comma, moreover, comma. The Greeks began their sentences with their kai, the Hebrews began their sentences with their w’, and the Romans began their sentences with their atque. It’s natural. You can overdo it, of course. But then, you can begin too many sentences with notwithstanding or inasmuch as. As, for instance, two.

The monks who introduced the Roman alphabet into England, to evangelize the pagan Saxons and teach some of them to read, were faced with an obvious problem. How do we use these Roman letters to signify sounds and sound-combinations that don’t exist in Latin? They actually did a phenomenally good job of it. They heard the Saxons pronouncing words—quite a lot of them, and some very common words among them—that began with an aspirated w. Round your lips, make as if you’re going to hwistle, blowing air out and saying witch. Did you hear it? You just turned it into which. Do the same with wail. Shazzam!  You have pronounced whale.

The monks were sensible and careful men, so they placed the h before the w, hwere it really belonged. Our modern wh-words were, in Anglo Saxon, hw- words. What was one such: hwaet.

Hwy is that important? Well, suppose we want to find relatives in Greek and Latin. We want to know hwich consonant really begins the word. In this case it is h. So we apply Grimm’s Law. That law says: Never gather salad greens from a witch’s back yard. Actually, it instructs us, among other things, that words in Germanic that begin with h are the cousins of words in Greek and Latin that begin with c (k). So it is with hwaet. But in Latin, hwen a c sound is followed by the consonant w, the result is spelled qu-. There’s our cousin: Latin quod, what (Grimm also tells us that Germanic d = Latin t). A related word, whit, recalls Latin quid, as anyone with a hwit of wit (not related to whit or what) would conclude.

Again I open my Bible at random: “But I say unto you, I will not drink henceforth of this fruit of the vine, until that day when I drink it new with you in my Father’s kingdom.” And again: “But woe unto you, Pharisees!” And again: “But I know him, for I am from him, and he hath sent me.” If it is good enough for Almighty God, it is good enough for a freshman, certainly.

There never was such a rule in English grammar. Nor was there ever such a rule in classical Greek, or in Latin. It is the quick and natural way to begin an adversative sentence, one that shifts direction from the previous, or contradicts it, or backs away. Unless you have a particular reason for preferring the slower comma, however, comma, not only may you begin a sentence with but: you really should do it. I tell my students this all the time. But they are slow to turn from their old ways, the reprobates.

The word is very old indeed. It was our original general word for growth, of plants, children, animals, nations, whatever. It is cognate with German wachsen, to grow. It used to be a strong verb, too—the German linguist’s term for verbs that don’t fool around with piddly dental past tenses, but change their own darned vowels, take that! The Anglo Saxon weaxan had the past weox: he weox eald, he grew old; cf. German er wuchs, he grew. Does it have any relations in Italy and Greece? Quite a few. The old Romans used the letter v for the sound we denote by a w: so that Caesar’s boast, Veni, vidi, vici, might still at that time have been pronounced wainy, weedy, weeky, which does not actually impress the ear with power; and that may explain why he had to cross the Rubicon. In any case, we look for Latin cousins of our w words among their v words. And sure enough, we have vigere, to thrive; and the kinfolk in that clan, from which we derive Modern English vegetable and vigor. So if a man waxes vigorous, we can say he waxes waxy: a heck of a lot of growing going on there.

“One must lift the tip of one’s nose to the cup, just so,” says Monsieur Lemonnier, removing his pince-nez for the purpose, “and flare one’s nostrils so as to let the bouquet of the wine enter into one with the most effective effluvia.”

“Enter into one what?” says Bobby Joe.

The indefinite you is perfectly fine for almost all kinds of writing. Oh, not for the description of scientific experiments, I grant. “Well, first you drip this red stuff here into that there tube”—I don’t think that will do for a journal article. But for popular writing, and even for conversational writing admitting of a high intellectual tenor, the use is admissible and often preferable to the alternatives. In those cases, it beats the heck out of all those ones.

But the Latin word for fruit, frux, wasn’t related to what you do with fruit when it’s ripe. It was related to what the tree does: it bears fruit. We borrowed words directly from the Latin for the sugar that fruit contains, fructose, and for the virtue of stretching the fruit of your labors, frugality, and for making something else bear a lot of fruit, fructify. We had already had the word fruit, from the Norman French invaders; that word came from the Latin fructus.

Do we have any words in English that the fancy-dancy French fruit displaced? After all, there were fruit trees in England before the French got there, and it doesn’t seem likely that the Saxons said, “Go pick me one of those things there that hang from that there tree.” What does Grimm’s Law say? Never eat an apple from an ugly old lady. Actually, it relates Germanic consonants to their Latin / Greek kinfolk. Grimm’s Law says that Latin f = Germanic b. We are looking, then, for a Germanic word beginning with b, followed by r and a vowel (or a vowel and r; they change places a lot), followed by a back-of-the-mouth consonant. Is there such a word? Sure: Old English byrig, mulberry: Modern English berry. But that wasn’t the old word for fruit in general. That old word was aeppel: Modern English apple. That’s the origin, there, of the idea that Adam and Eve ate an apple. What they ate was a fruit. It could have been a peach or a pear or a pomegranate—or an apple.

Blessed are the poor in spirit, for theirs is the kingdom of heaven.
Those who mourn are going to be happy too, because they will be comforted.
The inheritance of the earth will belong to the meek, and that will be most fortunate for them.
People who hunger for righteousness will experience a favorable state of affairs . . .

Anyway, Thesaurus polytropus is a wily old dinosaur. He doesn’t attack head on. He baits his prey by leaving in open view the carcasses of words, and just when you think you’re going to enjoy an easy meal—no hunting, no skinning—pounce! He’s got you by the throat.

The thing is, very few words are really synonymous with one another. This makes English especially baffling for non-native speakers. English is phenomenally rich in words, from the Germanic foundations, from the Viking variants, from the French by way of the Norman Conquest; words borrowed or invented from Latin and Greek from the Renaissance to this day; we even borrow ways of making new words. No language has as many words as English does. No language is even close.

So we use words that are sort-of-synonymous, but assign them to special areas of meaning, with differences in nuance. Look at a few “synonyms” for big: large, vast, massive, enormous, great, gargantuan. Put them in sentences:

Elsie is a big woman on the committee.
The distance between Earth and its moon is vast.
The elephant’s shoulders are massive, weighing hundreds of pounds.
Mr. Calhoun wears large pants.
The football player put away a gargantuan supper.
It’s a great deal.

Now change them around:

Elsie is a large woman on the committee.
The distance between Earth and its moon is massive.
The elephant’s shoulders are vast, weighing hundreds of pounds.
Mr. Calhoun wears gargantuan pants.
The football player put away a great supper.
It’s a big deal.

Different, eh?

The word is a distant cousin of ancient Greek thymos, meaning “spirit,” not in the sense of one’s soul, but rather what we’d call drive, ambition, fire. How do we get from there to here? Grimm’s Law helps, as always. Grimm’s Law says that if you sprinkle fairy dust over your shoulder—no, it doesn’t say that. It relates the Proto-Indo-European th to Germanic d. In one of these essays I’ll explain why. So what shows up in Greek and Latin as th will reliably show up in Germanic as d. Hence all we have to account for now is the nasal consonant m.

“But wait!” says a homeschooled lad in the sixth grade. “You mentioned Latin th. But there aren’t any original Latin words with a th. Everybody knows that!” Quite so, young man. And that requires explanation. When a sound should show up in a language but doesn’t, we have two ways of accounting for the absence. One is that the sound simply dropped out. People found it hard to say, maybe, or they figured they could do without it, or nearby speakers of a different language didn’t use it: so we no longer pronounce the k in knee. The other is that the sound was transformed into another and somewhat similar sound. Children help us out here. When my son was a very little boy, he’d say “fin” for “thin” and “vat” for “that.”  He was substituting a labiodental unvoiced spirant (f) for the interdental unvoiced spirant (th). That sure clears everything up! Try it, though, and you’ll see how it could happen. The Romans had no words beginning with th, but they did have a lot of words beginning with f, not all but some of which corresponded to Greek words in th. So then: Greek thymos = Latinfumus, smoke; English fume comes from the French, in the Middle Ages.
Back to dust: what happened to the m? Well, we know it was there, but by the time of Old English it had dropped away. But the Germans, a little more isolated, preserved the nasal consonant: Dunst: dust, mist, fume. All of which suggests a revision to the old folk song:

Are you going to Scarborough Fair?
Parsley, sage, rosemary, and dust –

No, it doesn’t work for me either.

Il figlio del re d’Inghilterra (Italian)
Le fils du roi d’Angleterre (French)
Der Sohn des Koeniges von England (German)

In each case, the possessive applies to the noun alone.  In the Romance languages, the possessive must be marked by a prepositional phrase: The son of the king.  In German, the possessive is typically marked twice, by the word order, and by our well-known s on masculine or neuter singular nouns.  It’s how we form our possessives: we add an s, but unlike the Germans, we add it to all nouns: It’s women’s night at the Colonnade.  The Germans can say, too, Des Koeniges Sohn, the king’s son, but that’s unusual, and for special emphasis.

What none of those languages can do is what we do all the time:

The King of England’s son.

Now, let’s stop and look at that.  He isn’t England’s son, the Prince of Wales; he’s the king’s son.  So why don’t we put the ending on the word King?  That would seem logical.  The fact is, that’s what we used to do:

The King’s son of England.

But that, you see, caused a little confusion.  Notice the difference:

The man on the street’s wife

The man’s wife on the street

That won’t do.  So we have a phrasal possessive.  But one shouldn’t be too reckless about using it:

The fellow I saw yesterday at the Burger King in Farmville’s Cadillac

Best then to use an adjectival phrase to show possession:

The Cadillac belonging to the fellow I saw yesterday at the Burger King.

What he was doing with a Cadillac at the Burger King, I’ll never know.