In the simplest terms, a knife is a tool designed to cut (let's not go down the rabbit hole of scissors, shears, chisels, etc. please). If it does not cut, it does not fulfill the specifications of a knife. I will not engage in arguments over degrees of sharpness or a knife that was sharp but is temporarily dull. If the object is created to be a cutting tool it should be sharpened, becoming a knife. If it was created as an artistic statement then it is an objet d'art. But "art" is subjective and we've had that conversation before as well. If the object was created with the intention of being a cutting tool, but is left less than sharp temporarily while photographs are taken for example, you can argue that it is a knife because it will be sharp. But it doesn't become a tool used for cutting until it is sharp. We have an emotional attachment to knives. They are beautiful and useful. But let's apply the concept to another common tool, the screwdriver. You can design it to be a screwdriver. You can make it out of pattern welded steel, heat treat it, put a fancy decorative handle on it, have it photographed, you can nuzzle it with your nose and call it cute little names if you like. But if at the end of the shaft is just a smooth round end, it is not going to screw anything but the customer.