The Art of Thought

"The first in time I shall call Preparation, the stage during which the problem was 'investigated ... in all directions';
the second is the stage during which he was not consciously thinking about the problem, which I shall call Incubation;
the third, consisting of the appearance of the 'happy idea' together with the psychological events which immediately preceded and accompanied that appearance, I shall call Illumination.
And I shall add a fourth stage, of Verification..."

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