Blake suggests that human beings do not ordinarily perceive reality in its fullest form. The image of the “doors of perception” presents perception as a filter: if it were cleared of its limitations, the world would appear not as narrow or finite, but as infinite.

The following sentence develops this idea by saying that people have “closed” themselves up and see through the restricted openings of a cavern. Blake therefore treats limited perception as partly created by human habits, assumptions and ways of thinking. The passage belongs to his wider concern with imagination as a means of seeing beyond conventional or restricted understanding.

The quotation is primarily epistemological because it concerns how people perceive and know reality. It also carries a metaphysical implication: Blake proposes that reality itself possesses an infinity that ordinary perception fails to recognise.

Full quotation

“If the doors of perception were cleansed everything would appear to man as it is, infinite.
For man has closed himself up, till he sees all things through narrow chinks of his cavern.”