A 'Top' is one who binds, dominates or inflicts pain. A 'Bottom' is one who is bound, submits or accepts pain. This is where alchemy comes in. Long before the invention of alternative algebras, magickians were investigating the idea of transmutation. Some people like sadism but not bondage.
Some people are simultaneously masochistic and dominant.
Some people like both sadism and masochism but with different people or at different times. Such people who are neither pure tops nor pure bottoms have a name of their own to be proud of, 'switches'. Pleasure is not a single quality. There are many different sources of pleasure. If a sadist gains pleasure from inflicting pain, that doesn't mean the masochist must lose pleasure from receiving it.