Emotion
An involuntary reaction due to an active complex. (See also affect.)
On the one hand, emotion is the alchemical fire whose warmth brings everything into existence and whose heat burns all superfluities to ashes (omnes superfluitates comburit). But on the other hand, emotion is the moment when steel meets flint and a spark is struck forth, for emotion is the chief source of consciousness. There is no change from darkness to light or from inertia to movement without emotion. [“Psychological Aspects of the Mother Archetype,” CW 9i, par. 179.]
Affect
Emotional reactions marked by physical symptoms and disturbances in thinking. (See also complex and feeling.)
Affect is invariably a sign that a complex has been activated.
Affects occur usually where adaptation is weakest, and at the same time they reveal the reason for its weakness, namely a certain degree of inferiority and the existence of a lower level of personality. On this lower level with its uncontrolled or scarcely controlled emotions one … [is] singularly incapable of moral judgment. [“The Shadow,” Aion, CW 9ii, par. 15.]
© from Daryl Sharp’s Jung Lexicon, reproduced with kind permission of the author.