What makes a punishment a punishment?

Just what makes something a punishment?

In the BDSM world of fetish, submission, and masochism, what really separates an activity from being kinky vs. a punishment?

While I'm sure to the vanilla world there are many things that would seem like a punishment, such as corporal punishment, humiliation, orgasm denial, or chores.  When these become the norm, what is the deciding factor?

I have thought about this question a lot over the years... how to answer that ever-asked question of "if I beat him, he likes it, so how is that a punishment?"

The common characteristic that make punishments what they are I believe is the introduction of meaningless hardship.  Hardship that doesn't have to be there but is added in order to create suffering and serves no beneficial purpose beyond that.

If the sub already does the chores, restricting his hand movement by attaching his wrists to his balls increases difficulty, discomfort, and creates a sense of despair as he knows his performance will be poor, leading to increased punishment.

If the sub is already well-disciplined and well-controlled at keeping his hands off of his penis and controlling his erections, adding a chastity device or KTB drives home the point.

Forcing the sub to sleep in a cage instead of a bed is another means to inflict suffering.

Corporal punishment can be performed on such a level where the aftermath will haunt them for days (this usually goes well-beyond enjoyable kink). 


Some of the longest-standing examples throughout history that mirror a similar sentiment are the punishments from legend/mythology in ancient Greece. 

Sisyphus was able to cheat death twice.  His punishment was to roll a giant boulder up a hill.  When the boulder reached the top, it would roll back down and he would begin again... for all eternity.

Tantalus did a lot of pretty fucked up shit.  His punishment was to stand in a pool of water up to his neck below a fruit tree.  If he reached for the fruit, the branches moved away.  If he leaned forward to drink, the water would lower out of reach.

Prometheus took fire from the gods and gave it to man.  This gave man knowledge and made them too similar to the gods.  His punishment was to be chained to a rock and every day a giant eagle would come and rip out his liver and every night it would grow back again.

The common themes:  incredible suffering with a pointless state of existence.