Anyway, this is what happens when you try and conceptualize the Basic 4 D&D classes as species with an eighth grader's understanding of the theory of Evolution.
So in the beginning, there were only four classes, the Fighter, Thief, Magic-User and Cleric. And for sake of argument, let's assume that the race-as-class ones such as Elf, Dwarf, and Halfling don't exist.
But then time progressed, and each class began to sub-divide. Here are the basic lineages of these four base Ur-classes.
A DEX fighter, on the other hand, is more for someone who wants to avoid being hit, and maybe make more ranged attacks. This line is where fancy fighters like Duelists, Swashbucklers, Pirates and other stuff comes from.
The Magic-User is the root of this line, and splits into various branches. I already explained the differences between Warlock, Sorcerers and Wizards here, so I won't waste any time with that.
Then from their, the Cleric brought forth the Paladin, the Cleric as we know them today, and the Squishy Priest. The Paladin is the Cleric with the moral inflexibility and the damage dealing ability turned up to 11, the Cleric is mostly unchanged, minus the fact that they can now rise to the level of Wizard without any of the unfortunate side-effects.
As for the Squishy Priest, I just included that to include all the other Cleric inspired classes, such as this one and others.
But now, let's get creative.
So do you remember Throne of Salt? Well, the post that initially inspired this can be found here. It was a class about being a chubby, jolly monk that punches people using magical martial arts. But if you read the monk's magical martial arts moves, you find one similarity. They are written with the GLOG system, the same one that Wizards from the same system use.
So this lead me to a revelation. Wizards use their minds and souls to cast spells. But their is another creature, the Muscle Wizard. Muscle Wizards use their bodies instead of their minds to cast spells.
And you know who else uses their body to perform magical feats, such as running super fast, catching arrows out of the air, and other Hong Kong action movie bullshit? Monks.
So, here's an idea. Monks are just Muscle Wizards who are descended from the opposite side of the Fighter family tree.
And once this line of theorizing gets started, where does it end. For example, the Humble Bard. Hated by large sections of the OSR for reasons that were never made clear to me. Perhaps its the type of players who want to play Bards? Regardless, I don't even have to think this one through, as Arnold K already did here.
To quote the man, "Bards are sorta lame. Yet Noise Marines are awesome. This is perhaps unfair, but it is true.
I propose that bards are not a class on their own, but merely Thieves that have multiclassed with Some Sort of Undiscovered Wizard, which I will now attempt to elucidate, by inferring from the parts of the bard that are awesome."
Also, just for the record, this was just my attempt to come up with a reason to include Monks in standard Medieval games. You're welcome, by the way.