It is difficult for the mind, when actuated by any passion, to confine itself to that passion alone, without any change or variation.
 David Hume, A Treatise of Human Nature (1738). copy citation

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

Context

“Grief and disappointment give rise to anger, anger to envy, envy to malice, and malice to grief again, till the whole circle be compleated. In like manner our temper, when elevated with joy, naturally throws itself into love, generosity, pity, courage, pride, and the other resembling affections. It is difficult for the mind, when actuated by any passion, to confine itself to that passion alone, without any change or variation. Human nature is too inconstant to admit of any such regularity. Changeableness is essential to it. And to what can it so naturally change as to affections or emotions, which are suitable to the temper, and agree with that set of passions, which then prevail?” source