Full Idea
In a republic ambition is pernicious, but in a monarchy it has a good effect; it gives life to that type of government. Its advantage lies in that it is not dangerous, because a monarchy can continue to restrain it.
Gist of Idea
Ambition is good in a monarchy, because the monarch can always restrain it
Source
Baron de Montesquieu (The Spirit of the Laws (rev. 1757) [1748], 03.07)
Book Reference
Montesquieu,Baron de: 'Selected Political Writings', ed/tr. Richter,Melvin [Hackett 1990], p.130
A Reaction
That is sometimes offered as a defence of the very weak British monarchy.