Swords and Swordplay Part 1 | Part 2 | Part 3 | Part 4
Militia and Military Training
Training is the key element here, but that doesn't mean that only the upper classes would have wielded a sword. Anyone with military (or militia) training may have received at least some level and quality of sword instruction. This means that many commoners knew how to use a sword, and while not every peasant--or even most of them--would have been a swordmaster, militia training has been a common practice in many places throughout history.
However, swords are often expensive equipment. While that will depend on the resources your culture has, as well as what types of swords they use, the cost can be prohibitive to commoners. Swords were also often passed down through families, so if your character has a family history of military service, they could certainly own a sword (or swords). Consider the history of your world. Because military service often means training with and possession of a sword, cultures with more ex-soldiers (often a result of lots of fighting) may have more swords floating around. Of course, you culture may also reclaim any sword belong to a soldier who leaves the ranks, so that they can equip new recruits (and possibly save resources).
Once you've established how common swords are in your background, training becomes the biggest issues. Historically speaking, there were plenty of people who wanted other people dead. Or at least, wanted what the other people had, and since those "other people" weren't willing to just give it up... Yeah. Commoners fought with what they had--be that a sword or some other weapon--and they spent at least some of their time learning how to fight with what they had. That isn't to say they were necessarily up to the task of putting down better trained, better equipped marauders, but I doubt they were all that surprised when the marauders showed up.
Imagine living in the middle of nowhere in an era where you couldn't call emergency services, or even the neighboring village. Even if you sent the message that you were being attacked by pigeon (as opposed to horse- or foot-bound messenger) or smoke signal or magic, you've got a bit of a wait before anyone can travel the distance to come and help you. No ability to defend yourself means possible death, injury, kidnapping, or loss of anything you may own. Do you really think people would live like that without developing some defense? Would you? Or would you instead make sure that the people in your village could put up at least some sort of defense? And this is equally true in rural villages or bustling urban centers. Both present their own sets of dangers and the types of weapons and techniques would have varied, but if you're likely to be attacked you learn to defend yourself out of sheer survival instinct.
Some swords, notably the rapier, were specifically designed for urban civilian self-defense and were not meant for use on the battlefield. The difference is one of armored and unarmored opponents. Since people didn't generally walk around cities in full armor for the sheer fun of it, civilians weren't likely to need a broadsword to defend themselves. Rapiers are thrusting weapons, and thrusting weapons require less strength, and rely on speed and precise aim, while cuts rely more on strength and momentum. Deep puncture wounds caused by thrusting weapons are also more difficult to treat, medically speaking, and if you don't need to get through the armor first, a rapier can do a lot of damage.
What this also means is that, in addition to militia training, there were places where civilians could go to be trained in the use of such weapons. Having a rapier you can't use strapped to your hip is much more dangerous to you than to anyone else. The advent of the rapier for civilian self-defense mostly affected urban areas, where it's generally easier to find weapons and training, but obviously that will be influenced by your own worldbuilding.
Next post, we'll talk about cutting vs thrusting, and a bit about mounted combat.