Concept

Necessary vs Contingent Being

Intro

Look around the room. The chair you are sitting on did not have to exist; it was made by someone, sometime, out of wood or steel that did not have to exist either. The tree the wood came from did not have to exist. The seed the tree grew from did not have to exist. You did not have to exist; your parents did not have to meet. Earth did not have to form. The whole universe might not have come into being.

Everything we have ever observed has this same shape. Philosophers call it contingent being. Something is contingent if it exists, but it could just as easily not have existed. Its existence is borrowed; it depends on something else holding it up.

Now ask a deeper question. Can everything be contingent? If every single being depends on something else for its existence, then the whole chain is borrowing existence forever, but no one ever actually has any to lend. Imagine a long line of people each saying, "I can give you a dollar as soon as I get one from the next guy." If that line goes on forever with no one who actually has a dollar to start with, nobody gets a dollar. Existence works the same way. A chain of pure dependence with no independent ground gives you nothing at all.

So either nothing exists (false, since things plainly do), or somewhere there is at least one being whose existence is not borrowed. Something that does not depend on anything else. Something that cannot fail to exist. Philosophers call this a necessary being.

That is the whole hinge of the argument from contingency. A necessary being is not just one more thing in the world; it is the kind of thing that has to exist by the nature of what it is. Classical theism identifies this being as God: not a being among beings, but Being itself, the source from which everything contingent has its existence.

The page walks through the careful version of the distinction (the technical modal logic), Leibniz's classic formulation, Aquinas's Third Way, the modern objections (could the universe itself be necessary? could existence be just brute fact?), and the standard responses. The argument is not "the universe began, therefore God." That is a different argument (the Kalam). This one is, "the universe is the kind of thing that could fail to exist, therefore something else, which cannot fail to exist, must ground it." Two different inferences, two different forms of cosmological reasoning.

In full

The distinction between necessary and contingent being is the central modal-metaphysical distinction in classical theism and the load-bearing premise of every cosmological-from-contingency argument. A contingent being is one whose existence is not necessary, it could have failed to exist, and depends on something else for its being. A necessary being is one whose existence is necessary, it could not have failed to exist, and is independent of anything else. The argument from contingency runs that the chain of contingent beings cannot terminate in another contingent being or in nothing, it must terminate in a necessary being, which classical theism identifies with God.

Definition

Two beings, two modal profiles:

Contingent being, exists, but might not have existed; its existence is possible but not necessary. Formally: ◇¬x exists. Depends on something else (a cause, a sustainer, a sufficient reason) for its existence. Everything in the observable universe, every star, every person, every quark, appears to be contingent.
Necessary being, exists, and could not have failed to exist; its existence is necessary. Formally: ◻x exists. Independent: does not depend on anything else for its being. Self-grounded.

A neighboring distinction: aseity (from itself), the property of having one's being from oneself, not from another. A necessary being is a se; contingent beings are ab alio (from another). See Ipsum Esse Subsistens.

Historical development

Plato (Timaeus), distinguishes the eternal Forms from contingent sensory things. Proto-form of the distinction.
Aristotle (Metaphysics XII), the Unmoved Mover is necessary in the sense of being everlasting and uncaused; not yet the modal-logical formulation.
Avicenna / Ibn Sina (Al-Shifa, c. 1027), the first fully developed Necessary Being / contingent being distinction in Islamic philosophy. The Necessary Being is wajib al-wujud (necessary of existence); contingent beings are mumkin al-wujud (possible of existence). His argument from contingency anticipated Aquinas.
Anselm (Proslogion, 1078), the ontological argument treats God as a being whose non-existence is impossible.
Thomas Aquinas (Summa Theologiae Ia, q.2, a.3, 1265-73), Third Way: from contingency. Things in nature are contingent (they come to be and pass away); not everything can be contingent (else nothing would now exist); therefore some necessary being exists; this all call God.
G. W. Leibniz (Monadology, 1714; Theodicy, 1710), the Principle of Sufficient Reason demands an explanation for every contingent fact; the chain terminates in a necessary being whose explanation is internal.
Samuel Clarke (A Demonstration of the Being and Attributes of God, 1705), Boyle Lectures formalization of the Leibnizian cosmological argument from contingency.
Alvin Plantinga (The Nature of Necessity, 1974; God, Freedom, and Evil, 1977), modal-logical reformulation; necessary existence as a great-making property in the modal ontological argument.
Joshua Rasmussen, Alexander Pruss, Robert Koons (early 21st c.), contemporary defenders of contingency arguments using modern modal logic.

Major theistic uses

Aquinas's Third Way (cosmological from contingency)

Some things are contingent (they exist but might not have).
If everything were contingent, then at some past time nothing would have existed.
But if at any past time nothing existed, nothing would exist now (out of nothing, nothing comes).
Things exist now.
Therefore not everything is contingent, some necessary being exists.
This being is God.

The textually disputed move is step 2 (the "all contingent ⇒ past gap" inference); modern reformulations often skip it and argue directly from the dependence-structure of contingents.

Leibnizian / Modern contingency argument

Every contingent fact has an explanation (Principle of Sufficient Reason; see Principle of Sufficient Reason).
The totality of contingent facts is itself a contingent fact.
Therefore the totality requires an explanation.
The explanation cannot be internal to the totality (no contingent fact explains itself or the whole).
Therefore the explanation is a necessary being.
This being is God.

See Contingency Argument.

Modal Ontological Argument

Plantinga's reformulation of Anselm:

It is possible that a maximally great being exists. (◇MGB)
A maximally great being has necessary existence in every possible world.
Therefore in every world, MGB exists. (S5: ◇◻P → ◻P)
Therefore in the actual world, MGB exists.

See Modal Ontological Argument and Modal Logic.

Necessary Being is an Intelligent Mind

Hybrid argument (developed in ris3n's notes): the necessary being identified by the cosmological argument has, on further analysis, the attributes of personhood, intentionality, and intelligence, making it not merely a metaphysical X but the God of classical theism.

See Necessary Being is an Intelligent Mind.

Atheistic alternatives

If a necessary being is denied, the chain of contingent beings must be explained otherwise. Three standard atheist options:

1. Brute fact

The universe (or a primordial state) is a brute, unexplained fact. Russell to Copleston (1948 BBC debate): "I should say that the universe is just there, and that's all." This violates the PSR, defenders argue PSR is not obvious and brute facts are tolerable.

2. Infinite regress

The chain of contingent causes extends infinitely backward, with no first cause. Defenders (Hume; some contemporary atheists) argue an actual infinite of past causes is coherent. Critics (William Lane Craig, defending the Kalam variant) argue the infinite regress fails to explain contingency; the whole chain is still contingent and unexplained.

3. Self-causation / necessary universe

The universe itself is the necessary being. Defenders include some modern naturalist metaphysicians. Critics note that the universe appears highly contingent (it could have had different constants, different laws, different initial conditions); making it necessary requires that every feature of it be necessary, which is implausible.

Strengths and weaknesses

Strengths:

The distinction is intuitively forceful, the cup on the table might not have existed; whatever explains it must (eventually) not have that property.
It tracks rigorously in modern modal logic (S5).
It supports a family of mutually-reinforcing arguments (Aquinas's Third Way, Leibniz, Pruss-Koons, modal ontological).

Weaknesses / contested points:

The very coherence of necessary existence is denied by some (Hume, Mackie): the assertion "X exists necessarily" is treated as conceptually confused.
The PSR, load-bearing for the Leibnizian version, is itself contested.
Even granting a necessary being, the further identification with the God of theism requires additional argument.
Quantum-mechanical events that appear uncaused are alleged counterexamples to "every contingent has a cause" (defenders reply that QM events are not strictly uncaused, the quantum vacuum is a causal substrate).

Christian engagement

The necessary / contingent distinction has been a central plank of Christian metaphysics from Augustine through Anselm, Aquinas, the medieval scholastics, the Reformed scholastics (Turretin), and contemporary analytic theology. God's aseity, self-existence, is among the divine attributes most emphasized in classical theism. Scripturally it is anchored in Exodus 3:14 ("I AM THAT I AM"), John 5:26 ("the Father has life in himself"), and Acts 17:25 ("nor is he served by human hands, as if he needed anything").