Wikipedia
The principle of sufficient reason states that everything must have a reason or a cause. The modern formulation of the principle is usually attributed to Gottfried Leibniz, although the idea was conceived of and utilized by various philosophers who preceded him, including Anaximander, Parmenides, Archimedes, Plato and Aristotle, Cicero, Avicenna, Thomas Aquinas, Anaximander of Miletus, and Spinoza. Some philosophers have associated the principle of sufficient reason with " ex nihilo nihil fit"., Hamilton identified the laws of inference modus ponens with the "law of Sufficient Reason, or of Reason and Consequent" and modus tollens with its contrapositive expression.
Usage examples of "principle of sufficient reason".
All possible experience therefore, that is, all objective knowledge of phenomena with regard to their relation in the succession of time, depends on 'the principle of sufficient reason.
Hence all attempts at proving the principle of sufficient reason have, according to the universal admission of all competent judges, been vain.
But the further inference from the nerve stimulus to a cause outside of us is already the result of a false and unjustifiable application of the principle of sufficient reason.