I have observed in considering the nature of ambition, that the great feel a double pleasure in authority from the comparison of their own condition with that of their slaves; and that this comparison has a double influence, because it is natural, and presented by the subject.  When the fancy, in the comparison of objects, passes not easily from the one object to the other, the action of the mind is, in a great measure, broke, and the fancy, in considering the second object, begins, as it were, upon a new footing.  The impression, which attends every object, seems not greater in that case by succeeding a less of the same kind; but these two impressions are distinct, and produce their distinct effects, without any communication together.  The want of relation in the ideas breaks the relation of the impressions, and by such a separation prevents their mutual operation and influence.

To confirm this we may observe, that the proximity in the degree of merit is not alone sufficient to give rise to envy, but must be assisted by other relations.  A poet is not apt to envy a philosopher, or a poet of a different kind, of a different nation, or of a different age.  All these differences prevent or weaken the comparison, and consequently the passion.

This too is the reason, why all objects appear great or little, merely by a comparison with those of the same species.  A mountain neither magnifies nor diminishes a horse in our eyes; but when a Flemish and a Welsh horse are seen together, the one appears greater and the other less, than when viewed apart.

From the same principle we may account for that remark of historians, that any party in a civil war always choose to call in a foreign enemy at any hazard rather than submit to their fellow-citizens.  Guicciardin applies this remark to the wars in Italy, where the relations betwixt the different states are, properly speaking, nothing but of name, language, and contiguity.  Yet even these relations, when joined with superiority, by making the comparison more natural, make it likewise more grievous, and cause men to search for some other superiority, which may be attended with no relation, and by that means may have a less sensible influence on the imagination.  The mind quickly perceives its several advantages and disadvantages; and finding its situation to be most uneasy, where superiority is conjoined with other relations, seeks its repose as much as possible, by their separation, and by breaking that association of ideas, which renders the comparison so much more natural and efficacious.  When it cannot break the association, it feels a stronger desire to remove the superiority; and this is the reason why travellers are commonly so lavish of their praises to the Chinese and Persians, at the same time, that they depreciate those neighbouring nations, which may stand upon a foot of rivalship with their native country.