One of the first ever weapons, the knife (or "sharp rock" as it was called back then) has pretty much stayed the same through the centuries. The father of the sword, the knife is basically a piece of some hard material- say, steel, stone or bone- that's been carefully shaped into a fine edge and possibly a point.

Whereas the first knives were primarily used to cut, and evolved into axes (due to bastardization with a club), the pointed knife (hereafter called a dagger) used for stabbing soon evolved from spear, and evolved to the pickaxe

The cutting knife, originally made out of stones like flint that had been struck into an edge with harder rocks, was not often used as a weapon; rather, it was a tool for skinning and cutting meat, and sometimes used to cut branches. Though not used in the hunt, it could nonetheless be carried as a light side-arm ready for just when needed.

The dagger, however, had less use as a tool. It could be hammered into wood to break it, and could cut into the flesh and hides of mammals more easily than it's cuttng brother. This weapon had many of the benefits of the spear, but for it's length and the ability to be thrown, and had the advantage that it was easier to control and could be used as a tool.

Eventually, the knife and dagger merged together to form the knives we know today, using both a keen cutting edge and a decent point.

Of course, through each culture, each developed their own version of the knife; the Japanese evolved the Tanto, made for mainly slashing (of course with a point) and the Agiuchi, the former mainly made for self defence while the latter was to help in the fields and suchlike, while Europe just evolved various different types, such as the thin Stilletto used for stabbing and the marvelous bowie-knife used for cutting.

Nowadays, the knife is still used in many gangland cultures for combat, still favoured by some over the rapidly expanding use of the handgun; indeed, it's a common and more legal for of protection, from the various horrific flick-knives and jack-knives to the credit-card sized scalpel-blades that can be found. Almost all rely on either the blade or the point, normally not both. It's also scarily easy to make a makeshift knife or shank.

On the fields of battle, the knife was only really used by archers and such, use to fletch new arrows or as a side-arm to any troops. Two large knives were sometimes used by trained troops, but this merely made them look more deadly than they often turned out to be; it's also used as a weapon to parry other, for fencers and such.