the mind is a different organ by night and by day

The expression “the mind is a different organ by night and by day” names a change in perception rather than a change in events. After the narrator and Cousin Monica see Doctor Bryerly leave a room at Knowl late at night, their fear makes him seem almost supernatural; by morning, they can speak of his arrival as an ordinary fact. The phrase crystallizes the episode’s contrast between nocturnal apprehension and daylight understanding.

The Nighttime Encounter

The narrator and Cousin Monica watch from the gallery as a candle appears behind a door. Doctor Bryerly emerges carrying it, closes and locks the door, and walks away. The narrator describes feeling as frightened as if witnessing a sorcerer, while Cousin Monica locks the door from inside when they enter the room. Their actions show that the scene has unsettled them beyond the mere surprise of a visitor.

A Change in Understanding

The narrator stresses the limits of personal testimony, saying that the fear can be claimed with certainty for herself, while only supposing that Cousin Monica felt similarly. Yet by morning the first subject they discuss is Doctor Bryerly’s arrival. The visitor has not changed; the frame through which he is understood has. Night encourages a supernatural interpretation, while morning restores the event to ordinary recognition.

Narrative Significance

The expression distills the scene’s movement from fear toward explanation without declaring the nighttime reaction wholly false: the narrator genuinely felt terror, even as daylight altered its meaning. Its compact opposition between night and day makes perception itself the episode’s subject, and links the gothic uncertainty of the encounter to the later, matter-of-fact recognition of Doctor Bryerly.