Contingent beings are things that exist, but do not have to exist. Examples are my iphone, my car and me. Contingent beings depend upon upon other beings for their existence. In contrast, something is a necessary being if it exists, has always existed and has to exist; it cannot “not exist.” From the existence of contingent beings we can show that there must be at least one necessary being.

If a necessary being exists, its non-existence is said to be metaphysically impossible. An equivalent understanding is to recognize that the existence of a necessary being is metaphysically necessary. (Metaphysics is the branch of philosophy that studies the fundamental nature of reality.)

By definition, anything that has not always existed is contingent. Therefore, every person ever born is contingent. According to the current understanding of physics, electrons and other particles were formed soon after the Big Bang. Therefore, no electron is a necessary being. The same observation can be made of any physical object that we know about.

No contingent being can pop into existence on its own; it must be caused by something else. No contingent being exists without some source or cause of its existence. Our experience with reality confirms this. From nothing, nothing comes. “Nothing comes from nothing” (Latin: ex nihilo nihil fit) is a philosophical concept first argued by Parmenides, a Greek philisopher in the late sixth or early fifth century B.C. Lucretius (99-55 B.C.), a Roman philosopher, expounds on this concept in De Rerum Natura (On the Nature of Things), emphasizing that matter is necessary to create matter and that objects cannot spontaneously exist without a reasonable cause. In terms of modern physics, this understanding aligns with the law of conservation of energy, which states that the total energy of an isolated system cannot change.

(In discussion of popular science, we sometimes hear of particles popping into existence out of nothing. However, the devil is in the details, for there is always some preexisting entity [i.e., an underlying field for example] out of which these particles supposedly emerge.)

If contingent beings could exist without a cause, we would reasonably expect to witness things popping into existence from no cause. But we don’t. There is always an explanation (cause) of the existence of every contingent being. My parents were the cause of me, my grandparents were the cause of my parents, and so forth. But this obviously and intuitively cannot go on forever.

Consider every contingent being in the history of reality. Is there an infinite past of contingent beings? Current physics says “no”, that space/time began at some point. This means that some cause exists that explains the existence of all contingent beings. This “first cause” must exist necessarily meaning it cannot be contingent (dependent) upon some other cause or else it too would be a contingent being with another cause further up the chain.

There are only two possibilities for the reality of contingent beings. Either they exist or they don’t. If they exist, there is always an explanation of why they exist. The cause of all contingent beings cannot itself be a contingent being, or else it would be part of the contingent beings and also need an explanation. It cannot cause itself to exist for nothing can cause itself to exist. To cause itself to exist, it would already have to exist to do the causing.

An infinite regress is impossible.The reason philosophy avoids any “infinite regress” is that it leaves us with situations which are redundant, unanswerable, impossible, or useless. Aristotle first tackled this problem in his own philosophy, and it had a great influence on Aquinas’ cosmological arguments. The reason the universe “has to” stop at an “unmoved mover” (another way to say this is a first cause) is because we would never have a real answer to one of the most important philosophical questions: “Why is there something rather than nothing?” In other words, why is it that the universe exists at all? That is the question that the first cause attempts to answer.

Aquinas (1225-1274) offered a powerful version of the cosmological argument with this reasoning in his Summa Theologica. His Argument from Causation is the Second of his Five Ways. It concludes there must be a First Cause, an uncaused cause since an infinite regress is impossible. Here is Aquinas’ Second Way, his Argument From Causation:

A. Some things are caused.

B. Anything that is caused must be caused by something else since nothing causes itself.

C. There cannot be an infinite regress of causes.

D. There must have been a first cause, itself uncaused, and that is God.

This First Cause must exist necessarily to explain the existence of all contingent beings. This First cause we understand to be God. Every thing that is contingent needs a cause but God is an uncaused First Cause. This is why theologians understand God to be a necessary being. God exists necessarily; in other words, God cannot “not” exist. When we say that God is a necessary being, we are saying that it is impossible for God not to exist.