Please find below the source reference for the class:
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Also know and learn when he speaks: “Vor Nach those two.. etc” there he means the five words, Vor Nach Schwach Stark Indes and within these words lies all art of Master Liechtenauer and these are the basic foundation and the core of all fencing on foot or mounted, with armour and without.
By the word “Vor” he means that every good fencer should always gain the Vorschlag, may he hit or miss. And when Liechtenauer says “Strike and hurry to the man, rush in may it hit or miss”. This means, as soon he approaches his adversary by stepping or running, he should instantly attack as soon as he is sure he could reach him with either a step or a jump. Then he must attack to his head or to his body, without any fear to the opening which he can hit best. So he should gain the Vorschlag, and it is not important, if it directly hurts the adversary or not. He must also be sure with the correct measure of his steps, so that he may not step too short or too long.
If he now hits with the Vorschlag, so instantly follow through with the hit. However, if he defends the Vorschlag so that he turns aside or leads off the attack, be it a strike or a thrust, away from the intended opening with his sword, you should now, with the swords are still being in contact, feel or be aware whether he is soft or hard, weak or strong at the sword.
If he now feels how the adversary acts in his fencing, if he is strong or hard, in the very moment he realizes this he should, while the adversary is still protecting himself, become soft and weak and in the case of the adversary being weak, vice versa. To make sure that one cannot come to strikes, he should instantly execute the Nachschlag, that means that he attacks again while the other is still protecting himself from the Vorschlag, be it with a strike or a thrust. So he can employ different techniques for hurrying or rushing towards his openings and thus he is permanently in motion and very close to him and this should make him so irritated and confused that he is only busy protecting himself and cannot come to his own strikes. If one has to defend himself or has to be aware of the strikes which are directed against him, he is in much greater danger than the one who strikes at him, because he either can defend or be hit. And this makes it very difficult for him to gain the opportunity for his own strikes. So Liechtenauer says: I tell you truthfully, no one defends without danger, if you understood this, he will not come to strikes.
If these five words, which this teaching and all other fencing is based upon, are not adhered, then this is the reason why a brave peasant often defeats a master by winning the Vorschlag.
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Taken from the Nuremberg Hausbuch (MS 3227a), a German commonplace book thought to have been created some time between 1389 and 1494.