A man, when calm or only moderately agitated, is so different, in every respect, from himself, when disturbed with a violent passion, that no two persons can be more unlike
 David Hume, A Treatise of Human Nature (1738). copy citation

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Author David Hume
Source A Treatise of Human Nature
Topic calm passion
Date 1738
Language English
Reference
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Weblink http://www.gutenberg.org/files/4705/4705-h/4705-h.htm

Context

“But it is observable, that this repugnance may arise from a difference of degree as well as of kind; nor do we experience a greater difficulty in passing suddenly from a small degree of love to a small degree of hatred, than from a small to a great degree of either of these affections. A man, when calm or only moderately agitated, is so different, in every respect, from himself, when disturbed with a violent passion, that no two persons can be more unlike; nor is it easy to pass from the one extreme to the other, without a considerable interval betwixt them. The difficulty is not less, if it be not rather greater, in passing from the strong passion to the weak, than in passing from the weak to the strong, provided the one passion upon its appearance destroys the other, and they do not both of them exist at once.” source