This is mostly true with japanese swords, as they were thinner and the iron was not so good. On european medieval warfare this is half-truth. By hitting the edge of the blade, you have great possibilities of denting your blade but also of lodging the sword opponent, preventing the blade from sliding. Parrying with the flat plane is intuitively better, but the sliding of the blade can go directly to your fingers, unprotected by the hilt, so you can lose half a hand, break some finger if you carry mail or plate and of course, loose the weapon (thatâs why rings start to be added to the grip and this tendency slowly evolves into a single piece guard).
Now, from the dueling theory, egdge or half-edge is used but applying some sense. Iâll try to explain although is difficult to put into words.
First, we split the blade in 3 parts: Strong (near the grip), medium (the center), weak (the end point).
Letâs say your opponent throws an horizontal cut (Plane A). If you parry generating another plane, letâs say by intersecting your sword vertically (plane B), the following thing can happens (i wonât develop all the cases though, otherwise it will be impossible to read xd) :
- Your opponent has a greater blade parts than you: Your blade will move and you will be mostly sure striked. This is physics and momentum upon your hands, so it wonât matter how strong you are.
- Your opponent has a lesser blade parts than you: Mostly sure you will parry, the blade will receive the all the impact, your opponent will have his point end within angle and your are not preventing (if your blade is vertical) from his approach or the next attack.
So, how is it done the parry then? the answer is by creating a plane that matches a âconeâ between you and your opponent (you aim your point at the face of your opponent and you place your hands slightly outside your body). This way you never place a âorthogonal planeâ and any strong hit will mostly sure slid, throwing the opponent point end out of reach or making you gain blades part over your opponent.
This can be applied to most medieval swords (although with a shield, it changes a little bit of course).
After the heavy answer. Also bear in mind that weapon destruction during war was common and combatants usually carried between 3-5 weapons to use through the combat, without counting the ones that can take from the fallen ones.