QuestionsWhy is there something rather than nothing?An endless series of dependent beings has no reason to exist: there must be a necessary being
Why is there something rather than nothing?There is a reason

An endless series of dependent beings has no reason to exist: there must be a necessary being

Clarke's argument; the demonstration of the necessary being

Samuel Clarke 1675 · 1729English theologian and philosopher, a friend of Newton, who tried to demonstrate by reason the existence of a necessary being.
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What it claims

An independent being, existing by the necessity of its nature, has existed from eternity: this is the reason why there is something rather than nothing.

Why

If no being in the series exists by necessity, the whole series has neither cause nor reason: it would be determined by nothing.

The same idea through history
Gottfried Wilhelm Leibniz1714Leibniz states the same demand under the name of the principle of sufficient reason: there must be an ultimate reason outside the series of contingent things.
Samuel Clarke1705In the 1704 Boyle Lectures, published in 1705, Clarke starts from what has existed from eternity and argues that an infinite series of dependent beings cannot be self-sufficient.
Alexander Pruss2006Pruss takes up the structure of the argument with the tools of present-day modal logic and defends the principle of reason that supports it.
In short

"An endless series of dependent beings has no reason to exist: there must be a necessary being" is an argument by Samuel Clarke (A Demonstration of the Being and Attributes of God, 1705, 1705) on the question "Why is there something rather than nothing?" (answer: there is a reason). Its claim: An independent being, existing by the necessity of its nature, has existed from eternity: this is the reason why there is something rather than nothing. According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P4). AskPhilosophy presents 3 objections, 3 of them with a documented reply, and the original text behind each premise, checked word for word.

A Demonstration of the Being and Attributes of God, 1705
Valid with an implicit premise

In 1704 the English theologian Samuel Clarke gave the Boyle Lectures in London, published the next year as "A Demonstration of the Being and Attributes of God". He starts from a fact almost everyone grants: something has always existed. But what? An independent being, or a beginningless series of beings each depending on the previous one? Clarke holds that the second answer explains nothing: the whole series would have no outside cause, since it contains everything, and no reason in itself, since none of its members exists by necessity. He concludes that an independent being has existed from eternity. The text dates from 1705: the language is old, but the reasoning fits in a few lines. A caveat: Clarke then draws further attributes of this being (eternal, unique, intelligent); this page keeps to the first step, the one that answers the question "why is there something rather than nothing?"

P1Something has existed from eternity. Otherwise nothing would exist today: Clarke notes that this is already proved and granted on all hands.
P2So either one unchangeable and independent being has always existed, from which all others take their origin; or there has been an infinite succession of changeable and dependent beings, produced one from another with no original cause.
P3Such an infinite series, taken as a whole, has no cause outside it (it contains all that exists) and no reason within itself (none of its members exists by necessity, and where no part is necessary the whole is not). So it has "no reason at all" of its existence.
P4 · implicit premiseWhatever exists has a reason for its existence: either the necessity of its own nature or an outside cause. Chance is only a word.
Therefore an independent being, existing by the necessity of its nature, has existed from eternity: this is the reason why there is something rather than nothing.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P4, the computer finds a case where something has always existed, the infinite series of dependent beings has no reason, and no independent being is required.
Valid with P4. Without it, one could accept an infinite series that simply exists, with no reason. P4 is what Clarke finds obvious ("chance is only a word") and what his opponents dispute: for them, what is demanded of a part is not demanded of the whole.
Analogy. A chain of wagons coupled one to another, with no engine, moving forever. Each wagon is pulled by the one in front, but none pulls: Clarke asks what moves the whole chain. The image is ours.

Objections

3

Each objection is a conversation: click to see who replies and where the debate stands.

David Hume 1779 · attacks the conclusion

In the Dialogues, Cleanthes attacks Demea's version, which Hume links in a note to Clarke: whatever we conceive as existing we can conceive as not existing, so no being has a contradictory non-existence and the phrase "necessary existence" has no meaning. And if anything could be necessary, why not matter itself?

a defender replies
see the argument
Alexander Pruss defender of the argument · 2006
Pruss judges that this principle of Hume does not by itself give a satisfactory argument: it is not obvious that the totality of all existing things can be thought not to exist. He adds that numbers, propositions or properties would then have merely contingent existence, which seems absurd.
The debate goes on (our summary) Pruss himself notes the objector's rejoinder: numbers and propositions are abstract objects, whereas the necessary being at issue acts and is therefore not abstract (our summary).
Where the debate stands (our summary)The disagreement is about the meaning of "necessary being". For Hume only a contradiction makes an existence necessary, and there is none; for the defenders, necessity may lie in the nature of the being without passing through what we can conceive. The debate is unsettled (our summary).
David Hume 1779 · attacks premise 3

If the cause of each part of a series is explained, it is unreasonable to ask afterwards for the cause of the whole. Uniting the parts into a whole is merely an arbitrary act of the mind, with no influence on the nature of things: if we show the cause of each of twenty particles, we need not seek the cause of the twenty.

a defender replies
Alexander Pruss defender of the argument · 2006
Pruss answers that the Hume-Edwards principle (explaining each member explains the whole) is false. It depends on explanation adding up, which Gale and he dispute: explaining why each man is at the corner does not say why they are there together.
Where the debate stands (our summary)A disputed point: does explaining each member of an infinite series suffice to explain the whole series? Hume and Edwards say yes; Clarke, Gale and Pruss say no. No broad agreement (our summary).
Bertrand Russell 1948 · attacks premise 4

Russell, facing Copleston who takes up the argument of Clarke and Leibniz: the notion of cause comes from observing particular things, and he sees no reason to suppose that the total has a cause. The universe is just there, and that's all.

a defender replies
see the argument
F
Frederick Copleston defender of the argument · 1948
Copleston answers that saying there is no cause is not the same as saying we should not look for one: the claim should come at the end of the inquiry, not the beginning. And to say the world is simply there is already to answer a question that has meaning.
Bertrand Russell 1948
Russell replies with a comparison: every man has a mother, but we do not conclude that the human race has a mother. Moving from the parts to the whole is a change of logical sphere.
See the rest of the debate (1)
F
Frederick Copleston 1948
Copleston finds the parity false: he does not say that because each object has a cause the series has a cause of the same kind. He says the series of causes is an insufficient explanation of itself, so it needs a transcendent cause.
Where the debate stands (our summary)The core disagreement: must a reason be demanded for the whole, or may the world be a fact with no reason? Russell and Copleston did not agree, and the principle of sufficient reason remains the central issue (our summary).