Full Idea
Things could not have been brought into being by God in any manner or in any order different from that which has in fact obtained.
Gist of Idea
The actual world is the only one God could have created
Source
Baruch de Spinoza (The Ethics [1675], I Pr 33)
Book Reference
Spinoza,Benedict de: 'Ethics, Improvement of Understanding, Letters', ed/tr. Elwes,R [Dover 1955], p.70
A Reaction
Said to be a "notorious" proposition. This is a key idea in philosophy because it represents (like solipsism) one of the extremes - there is no such thing as contingency, and that all things are necessary. It is daft not to take Spinoza seriously on this.