While I don't want to (nor am qualified to) give a law lesson on weapons, as a customs officer I am required to know plenty about weapons laws as part of my job is to make a determination about the classification of goods and permit or deny their entry into Canada based on those laws.
The Criminal Code defines weapons, and to summarize it, includes anything deisgned or intended to be used as a weapon. Knives are not named specifically, but are included under "designed" or "intended" in most instances. For example, a butter knife is not designed to be a weapon, but if you stab someone with it, then you intended it so. Similarly, a switchblade is designed as a weapon (it has no practical manufactured use aside from that), but not necessarily intended as one if you just collect them. So why is one illegal, and the other not?
The asmwer is the Prohibited Weapons Orders, issued by Order-in-Council. The Criminal Code allows the government to issue orders-in-council prescribing certain weapons (and devices, and ammunition, and firearms) as prohibited, restricted, etc.
Most knives are ok. The ones that are not include:
- "Flick" knives (a knife that can be opened merely by centrifugal force, or flicking your wrist)
- Switchblades (a spring loaded or mechanically assisted knife that opens by button or release on the HANDLE ... buttons/levers on the blade are ok)
- Any device concealing a blade and which is disguised as an innocuous object (a lighter with a knife, a belt buckle with a knife, etc)
- A gravity knife
- Any bladed device with the handle perpendicular to the blade (a push dagger)
- A butterfly knife (again, opens by centrifugal force)
There is no limit on blade length, except as an exception to the above rules. For example, a sword cane is not illegal, because it is over 30cm in length. If you ever found a switchblade that was over a foot long, it would be legal as well.
These PWO's classify certain goods and make them illegal or illegal depending on what the government believes their designed use is. However, as I pointed out before, the "intended" use can also make something illegal. A concealed weapon is illegal, even if the item itself is legal. If I go walking around with a steak knife taped to my forearm under the sleeve, and get caught, I'll have a hard time explaining it's my favourite steak knife and I was going to a restaurant to order up a T-bone.
Which brings us to a final point -- something is only unlawful if it's caught. But my advice is, not to take chances. If you don't need it, don't carry it. I only carry a small folding pocket knife for work. I don't carry it any other time anymore. Odds are, if you end up in a knife fight with someone who knows how to use one, you are better off not having a knife of your own.
