What are the knife rules in Belgium? Owning any large knife OK? Carry any knife?
Owning isn't a problem for most types of knives, but there are some exceptions such as balis, autos, stilletos, gravity knives and hidden blades such as cane knives. Assisted knives are in a gray zone. What can be CARRIED is a different story. You can only carry knives that don't lock automatically, such as slipjoints (SAKs,...) but also Opinel knives f.e. They lock, but the lock does not engage automatically. Why they make that distinction is totally unclear to me. You càn carry fixed blades without size limit... But(!!) for everything you carry, you need to have a legitimate reason. What that is is not explained by law, so the police officer in front of you has a lot of power with regards to knives. To illustrate it: when you carry a fixed blade while hunting, you won't run into problems (or into cops for that matter

), but carry it openly in the cities and you'll have quite the problem. Some cities also have a zero policy, like Antwerp and Ghent. Over there, carrying a Victorinox Classic isn't even allowed...
So all in all, it depends. Do you live in a small town where most people know each other, it won't pose any problems if you carry a pocket knife or a small fixed blade. In cities or commercial centres...not so much.
In a forest, no one will bother you because you carry a knife. A legit reason would easily be camping, food prep,... but just don't carry it on your person. Carry it in your bag with your food instead. Same thing while transporting. Divers f.e. are allowed to carry a dagger with their gear while driving around, but it has to be in their gear. A few years ago, a man was fined and his dagger confiscated because it was lying in the back seat of his car during a alcohol check-up. According to the officer, it should have been with the rest of his gear in the trunk... So there you have it. There are some regulations, but in the end you're left to the mercy of the officer in front of you.