On the Knocking at the Gate, in Macbeth

From my boyish days I had always felt a great perplexity on one point in Macbeth. It was this: the knocking at the gate, which succeeds to the murder of Duncan, produced to my feelings an effect for which I never could account. The effect was, that it reflected back upon the murder a peculiar awfulness and a depth of solemnity; yet, however obstinately I endeavored with my understanding to comprehend this, for many years I never could see _why_ it should produce such an effect.

Here I pause for one moment, to exhort the reader never to pay any attention to his understanding when it stands in opposition to any other faculty of his mind. The mere understanding, however useful and indispensable, is the meanest faculty in the human mind, and the most to be distrusted; and yet the great majority of people trust to nothing else; which may do for ordinary life, but not for philosophical purposes. Of this out of ten thousand instances that I might produce, I will cite one. Ask of any person whatsoever, who is not previously prepared for the demand by a knowledge of perspective, to draw in the rudest way the commonest appearance which depends upon the laws of that science; as for instance, to represent the effect of two walls standing at right angles to each other, or the appearance of the houses on each side of a street, as seen by a person looking down the street from one extremity. Now in all cases, unless the person has happened to observe in pictures how it is that artists produce these effects, he will be utterly unable to make the smallest approximation to it. Yet why? For he has actually seen the effect every day of his life. The reason is -- that he allows his understanding to overrule his eyes. His understanding, which includes no intuitive knowledge of the laws of vision, can furnish him with no reason why a line which is known and can be proved to be a horizontal line, should not _appear_ a horizontal line; a line that made any angle with the perpendicular less than a right angle, would seem to him to indicate that his houses were all tumbling down together.