Since we're going into this meta-philosophical thing, your statement is false. If I call a tail a leg, dogs definitely have five legs. Unless they were of course born without a leg, or have otherwise lost one. There is no "reality" from a human perspective, it's all sensory input that goes through a lot of very subjective processing.

You can't _really_ categorize things. You can mostly sort of do it, but it never actually works out, because categories are human stuff, and human stuff is subjective and thus different depending on who you ask. Sometimes unclear even to the same person.

I can say dogs have five legs and the only reason most people will think I'm wrong is that society has come to categorize limbs based on function instead of length.