The principle of sufficient reason basically states that all things which exist or occur have a root cause. This cause can either be external — for example, a ball flying through the air because a foot kicked it — or internal, as with a person kicking the ball because he or she derives enjoyment from it. The principle first appeared in some form in the works of Parmenides, but the term was coined by Gottfried Leibniz, who is also most well known for the idea. Leibniz said that all truth is truth because either its negation implies a contradiction or because it is for the best.
A basic understanding of the principle of sufficient reason is that all things have a root cause or reason for their being. Essentially, it is the logical equivalent of saying that nothing comes from nothing. If a man jumps off a skyscraper, it isn’t sufficient to assume that it just happened; there has to be a cause somewhere. This cause can be an external factor or an internal factor.
An external factor comes from something other than the thing itself. For example, if the man jumps off a skyscraper, he may do so because he was threatened with torture by a captor if he were not to jump. The reason that everything falls towards the earth is because all matter in the universe is drawn to each other, and larger things have greater gravitational pulls. This principle aims to explain all arbitrary — seemingly unplanned — events through the idea that there is sufficient reason behind them.
Internal factors are often harder to determine, but they are essentially reasons that come from within the agent of a particular action. For example, the man may jump off a skyscraper because he has determined that existence has no definitive goal and he is not enjoying himself. The principle of sufficient reason implies that there are no unexplainable things or events.
Leibniz, the philosopher most famous for the principle of sufficient reason, said that all truths are dependent on one of two principles. The principle of contradiction states that there must be some truth if negating an idea or an event precipitates a contradiction. For example, Leibniz definitely either existed or didn’t exist — he couldn’t have possibly done both, so one must be the truth. Leibniz identified the second principle as the principle of the best, which states that anything that is true is so because it is for the best.