What does this quote mean?

“To define is to limit.”

Definitions clarify ideas but can also narrow them, especially when a label is treated as the complete reality of a person or experience.

Source note: The Picture of Dorian Gray, 1891 edition, Chapter 17; Lord Henry answers the Duchess of Monmouth’s question “What are you?” with “To define is to limit.”

“The universe is wider than our views of it.”

Reality exceeds any one viewpoint, so confidence in a perspective should leave room for what has not yet been seen.

Source note: Walden, Conclusion; Thoreau uses the sentence while arguing that familiar human views do not exhaust reality.

“We hear only the questions to which we are capable of finding an answer.”

The aphorism suggests that inquiry is limited by the conceptual capacities of the person asking, making intellectual growth partly a matter of becoming able to formulate and recognize better questions.

Source note: The Joyful Wisdom, aphorism 196; Thomas Common translation.

“It is a narrow mind which cannot look at a subject from various points of view.”

Intellectual flexibility requires seeing how the same issue can appear from more than one position before settling on a judgment.

Source note: Middlemarch; the narrator contrasts narrow judgment with considering a subject from several points of view.

“If the doors of perception were cleansed every thing would appear to man as it is, Infinite.”

Blake imagines habitual perception as a filter that narrows reality; cleansing it would reveal a less limited world.

Source note: The Marriage of Heaven and Hell, Plate 14; Blake’s prose-poetic argument about the limits and cleansing of perception.

“The unreasonableness of a thing is no argument against its existence, but rather a condition thereof.”

The aphorism separates the fact that something exists from the expectation that existence must be rational or well ordered.

Source note: Human, All-Too-Human, Part I, aphorism 515, “From Experience”; Helen Zimmern translation.