Even the 5 senses are arbitrary. Sensing where your body is positioned, where it's boundaries are, whatever tickling is, whatever itchy is, whatever sour is, whatever salty is, green, blue, etc. When we say 5, we are just saying where on the body they happen. Even though there are more axis on each and use different sensors. Warmth, cold, orgasm - is that really "touch" etc. Bunch of syscall enums maybe.