There are several previous threads on this topic.
This is something I wrote some years ago in response to a similar question on another forum.How would you know when you have gained enlightenment?
It is possible for an unenlightened person to be deluded about that, but an enlightened person could know by reading such books as "The Progress of Insight
It is also possible that an enlightened person would not know, due to lack of scriptural knowledge. It is very difficult to know whether another person has attained a certain stage or not, but a person with good scriptural knowledge might know with some degree of certainty. Only someone like the Buddha or Venerable Anuruddha would know by direct knowledge.
The Mirror of the Dhamma in the Mahaparinibbana sutta gives four criteria:
- Unshakeable confidence in the Buddha
- Unshakeable confidence in the Dhamma
- Unshakeable confidence in the Sangha
- Morality that is stainless and without defect
Anyone who kills, steals, commits sexual misconduct, or tells lies is definitely not a Stream-winner. I also doubt very much whether they would drink alcohol. I met several individuals in Burma, who I was confident had gained stream-winning or higher stages. Their conduct and mental demeanour was markedly different to most other good people, but anyone inexperienced in meditation or lacking in scriptural knowledge would not be able to distinguish them from an unenlightened person of good character.
This little story nicely illustrates the difficulty of measuring an enlightened person.
A certain monk was living in dependence on an Arahant. Living in dependence meant that he shared the same room as his teacher, did all the duties for him, and carried his almsbowl for him while walking behind for alms. One day, while walking for alms, the pupil asked, “Venerable sir, how can one know whether another person is an Arahant?”
The Arahant replied, “It is not easy, friend, to know if another person is an Arahant. Even if one lived in dependence on an Arahant, did all the duties for him, and carried his almsbowl while walking behind him for alms, one might not know that his teacher was an Arahant.”
Even when given such a broad hint as this, the pupil did not realise that his teacher was an Arahant. The Arahants have stainless minds free from all pride and conceit. They do not boast of their attainments, unless there is no other way to help people.