The Marginalists
Here is the origin of Pareto optimality:
We will say that members of a collectivity enjoy
maximum ophelimity in a certain position when it is
impossible to find a way of moving from that position very slightly
in such a manner that the ophelimity enjoyed by each of the
individuals of that collectivity increases or decreases. That is to
say, any small displacement in departing from that position
necessarily has the effect of increasing the ophelimity which
certain individuals enjoy, and decreasing that which others enjoy,
of being agreeable to some and disagreeable to others.
Manual of Political Economy
p. 261
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