The arguments for God

There is a way of presenting these arguments that makes them look foolish, and a way that makes them look compelling, and both are available for all five. This lesson uses neither. Each argument is set out in the form its best defenders give it, its valid structure is displayed, and then the single premise doing the work is identified, because that is where any real disagreement has to be.

Before starting, one thing to keep from lesson six. The intuition that the universe was made on purpose arrives free, in everyone, for reasons that have nothing to do with whether it is true. So the feeling that these arguments are obviously right, and the feeling that they are obviously silly, are both worth discounting.

The cosmological arguments

Two versions, often confused.

The Kalam argument, revived by William Lane Craig from medieval Islamic sources:

1. Whatever begins to exist has a cause.
2. The universe began to exist.
3. So the universe has a cause.

It is valid. Premise 2 is the one most discussed, usually by appeal to Big Bang cosmology, and it is weaker than it looks: the standard model describes the universe expanding from a hot dense state 13.8 billion years ago, and says nothing about whether that state was the beginning of existence. The singularity is where the theory breaks down rather than where time starts, and several live proposals have no beginning at all.

But premise 1 is where the real difficulty is, and it is easy to miss. Every case of causation we know is a case of rearrangement: things that begin to exist within the universe begin from pre-existing material, in time, under physical law. The premise generalises from that to the universe itself, which began, if it began, without pre-existing material and without a prior time for the causing to happen in. The inductive base does not obviously cover the case.

The contingency argument, from Leibniz, is stronger because it avoids all of this:

1. Everything that exists has an explanation of its existence, either in the necessity of its own nature or in an external cause.
2. The universe exists.
3. So the universe has an explanation.
4. If the universe has an external cause, that cause is a necessary being.

Premise 1 is the Principle of Sufficient Reason, and it is the load-bearing claim. Denying it means accepting a brute fact, something that exists with no explanation at all. Many philosophers accept exactly that, and the theist's reply is that accepting a brute universe while refusing a necessary being is arbitrary. The atheist's reply is that a necessary being is itself a brute fact with a nicer name. This is a genuine impasse and it is much more interesting than the Kalam.

Example. A critic answers the Kalam with "then what caused God?" Is that a good objection?

Not to the argument as stated, and understanding why is worth more than the objection. Premise 1 says whatever begins to exist has a cause, and the conclusion is a cause that did not begin, so no inconsistency arises: the argument is not "everything has a cause" and has not been made to except itself. The objection lands only if premise 1 is reformulated as the universal claim, which the defender never made. What survives is a better question, why an uncaused eternal deity is more acceptable than an uncaused eternal universe, and that is the contingency argument's territory. Notice how a popular objection can be both very common and aimed at a version of the argument nobody defends.

Now you. The Kalam concludes that the universe has a cause. How much further is it to the God of any actual religion?

Design and fine-tuning

The argument from biological design is the one everybody knows, from William Paley's Natural Theology (1802) and the watch found on a heath. It is also the one case in intellectual history where an argument of this shape was decisively answered, and that is why it matters here.

Paley's reasoning was good. The eye is an intricate arrangement of parts serving a function, the only known source of such arrangements was design, so a designer was the best explanation. Darwin supplied a second source, and the evolution course sets out the argument: heritable variation plus differential survival produces functional complexity with no foresight. The design inference was not refuted by philosophy but by the discovery of an alternative mechanism.

The lesson to carry is about inference rather than biology. "I cannot think of another explanation" is a fact about you, and Paley, who was neither careless nor stupid, was in exactly that position and was wrong. That should discipline how much weight anyone puts on the same move today.

Fine-tuning is the surviving version, and it is not about biology. Certain constants in physics appear to lie in narrow ranges outside which no complex structure would form. If the cosmological constant were substantially larger, the universe would expand too quickly for galaxies. Change the relative strength of the fundamental forces and stars do not burn or carbon does not form. The claimed narrowness varies wildly between authors and some of the famous numbers are disputed, but the phenomenon is taken seriously by working cosmologists, which the biological argument no longer is.

Stated in the machinery of lesson five: the observation E is a life-permitting universe. The claim is that $P(E)$ given a designer is high, and given no designer is tiny, so E strongly favours design.

Three replies. First, nobody knows the space of possible constants or its probability measure, so the "tiny" is asserted rather than computed. Second, a multiverse makes some life-permitting universe unsurprising, and lesson nine argued this is not automatically ad hoc. Third, and most important, the observation is selected: we could not have observed a universe that forbade observers. Lesson thirteen takes that up in full, because it is the objection that does the work.

Example. A defender of fine-tuning objects that the selection point is a non-explanation: of course we could only observe a life-permitting universe, but that does not explain why there is one. Is the objection right?

It is right that the selection point does not explain why, and wrong that this matters. The design argument is an evidential argument: it claims that the observation raises the probability of design. The selection reply attacks that claim rather than offering a rival explanation, by pointing out that the observation was guaranteed given that anyone is observing at all, so by lesson five its likelihood ratio is 1 and it cannot raise anything. Compare the firing squad: surviving twelve marksmen who all miss does call for explanation, which is why the analogy is popular, but the disanalogy is that you could have observed the alternative in the firing squad case, since surviving with a wound or hearing the shots is possible, and nobody observes a universe without observers. Whether the disanalogy holds is argued in lesson thirteen; here the shape of the disagreement is the thing to see.

Now you. Why does the reply above leave the contingency argument untouched?

The ontological argument

Anselm, in the Proslogion of 1078, argued from the concept alone: God is that than which nothing greater can be conceived; a being that exists is greater than one that does not; so if God existed only in the understanding, a greater could be conceived, which is a contradiction.

It has been reformulated many times, most influentially by Alvin Plantinga using modal logic: if it is possible that a maximally great being exists, then it exists. Validity here is not in doubt given the modal system chosen, and the entire question is whether the possibility premise is true, which turns out to be as hard as the original question.

Almost nobody is persuaded by it, including most theists, and Gaunilo pointed out within Anselm's lifetime that the same form appears to prove a greatest conceivable island. Its interest is as a test case for the machinery of this course: an argument can be valid, its premises can be hard to refute, and it can still fail to move anybody, which should prompt the question of what exactly is wrong. The usual answer, from Kant, is that existence is not a property that makes a thing greater.

Example. Apply the test from lesson nine to the fine-tuning argument: what does the design hypothesis forbid?

Very little, as stated, and that is its weakness rather than the narrowness of the constants. A designer might have made a universe with different physics and sustained life by other means, or made a small universe with one world rather than a vast and mostly empty one, or made life common rather than apparently rare. Since the hypothesis as usually offered does not tell us which, it fails to predict much, and a hypothesis that predicts little confirms weakly even when the observation fits. The way to strengthen the argument is to specify the designer's aims in advance and then check, which is what the more careful defenders attempt. The way to weaken it is to appeal to inscrutable purposes, which lesson nine showed cannot be done here and then withdrawn in lesson eleven.

Now you. Which of the five arguments is least damaged by the objections in this lesson, and why?