Leibniz is known among philosophers for his wide range of thought about fundamental philosophical ideas and principles one of which includes the principle of sufficient reason (that nothing occurs without a reason).
Leibniz stated : "There must be simple substances, since there are composites; for the composite is nothing more than a collection, or aggregate, of simples."
Leibniz was commited to the "principle of sufficient reason" , that for every state of affairs, there is a sufficient reason for it being so and not otherwise.