What is the purpose of the prison system at large?

Theoretically speaking, we are taught that prisons exist for reform and rehabilitation, with those sentenced to a prison term taking the time there to understand the gravity of their actions and working to change.

In reality, however, there might be a deeper part of the human psyche that views the prison as a place where the unwanted of society go to rot away, much like Britain sent off its most hardened criminals to Australia, never to be seen again.

Article 133 of the Constitution grants the President the power of mercy, which allows him to pardon, postpone, or substitute a sentence.