How do we know if purgatory is real?

I have been to the heavens of Christ, and know their beauty. In my Father’s house are many mansions. And I have been in purgatory—the purgatory of the Roman Catholics.

Do not scoff at those who have masses said for the repose of the souls of the departed. The souls are often conscious of such thoughtfulness. They hear the music, and they may smell the incense—most of all, they feel the power of the thought directed to them.

Purgatory is real—in the sense of being a real experience.

If you want to call it a dream, you may, but dreams are sometimes terribly real. Even those who do not believe in purgatory sometimes wander awhile in sadness until they have adjusted themselves to the new conditions under which they live. 

Should one tell them that they were in purgatory, they might deny the existence of such a state, but they would readily admit their discomfort.