Rule 9: "Never go anywhere without a knife."
Gibb's Rules NCIS
Beyond that, a knife is hard to define as it runs the full spectrum to small, blunt knives used to spread butter to things that are shortswords in all but name. The misuse of the name adds to confusion as many things called knives are, in fact, daggers ("knives" designed purely for use as weapons).
As a rule of thumb, a knife should have a blade below 6" long and be single edged and/or blunt ended and/or posses other features that indicate it is not primarily intended as a weapon. This is only a rule of thumb though - some authorities classify things like the machete, parang and golok as knives (since they are primarily tools), despite them being more or less sword sized. The Bowie knife too is a substantial piece of ironmongery but was designed with a variety of tool functions in mind.
Modern, "multi-function" bayonets are also hard to classify - they are primarily intended as weapons, but opinion varies as to whether they are fit to be used as such.
Superstitions involving knives, include the tradition that a token payment must always be made for a knife given as a gift, lest it sever relations between recipient and giver, that it is bad luck to pass a blade across a threshold, or to close a folding blade opened by another and that a knife must taste its owner's blood before it truly belongs to them.
Types of Knives
Game and Story Use
- These represent standard "backup" weapons in many settings. They don't to much damage and have lousy reach, but they are easily concealable and don't require ammunition. Plus you can use them as tools for many occasions.
- Until very recently - perhaps the last twenty years or so - pretty much everyone (certainly most men) would carry a knife of some kind. This was normally a fairly small blade normally intended as a tool, but in some trades and professions it could be a fairly substantial piece of ironmongery (Bowie's eponymous blade was primarily a tool, even if well known as a weapon). In the pre-modern period your pocket knife normally also did duty as tableware except in a very few cases.
- In most cases a pocket knife style blade won't even be thought of as a weapon. In places where weapons are forbidden (such as a Saxon lord's hall), everyone will still be carrying a knife…
- Knife superstitions might get involved in a game. Maybe you become more susceptible to maleficum if you enter a witch's home with a knife, or you can't use a knife proficiency unless you've injured yourself with the knife.