Philosophy of religion: a beginner’s guide to the big arguments

For years I have taught Jewish thought to adults in Jerusalem, and many arrive with one of two fears. Religious students worry that philosophy will take their faith apart. Secular students worry that I will try to sneak faith back in. I tell both groups the same thing: philosophy of religion is not a weapon for either side. It is the attempt to understand what religious claims mean, whether and how they could be known, and what follows from them. Believers and unbelievers have both done it brilliantly, often in conversation with each other.

This guide covers the questions you will meet first.

What kind of claim is a religious claim?

Before asking whether "God exists" is true, it is worth asking what kind of statement it is. Some philosophers treat it as a factual hypothesis, like a claim in cosmology. Others think religious language works differently: it expresses commitment, shapes a form of life, or points toward something no human concept can capture.

That last idea has deep roots. Maimonides, in the Guide of the Perplexed, argued that we can say nothing positive about God's essence. When we call God "living" or "powerful", we are really saying what God is not, or describing God's actions in the world rather than God's nature. Thomas Aquinas proposed a middle way: words like "good" apply to God by analogy, neither in exactly the human sense nor in a wholly different one. How we answer this question shapes everything that follows, because an argument for a God you cannot describe is a strange kind of argument.

Arguments for God

The cosmological argument starts from the existence of the world. One version, developed by the Muslim theologians of kalām and defended by al-Ghazālī, argues that the universe began to exist, that whatever begins to exist has a cause, and so the universe has a cause. Another, found in Aquinas's "Five Ways", argues that even an eternal world would depend on something that exists necessarily rather than contingently. In India, the Nyāya philosopher Udayana offered a series of proofs for God, including one from the world's being an effect that requires an intelligent maker.

The ontological argument, first set out by Anselm in his Proslogion in the eleventh century, tries to prove God from the concept alone. God is that than which nothing greater can be conceived. Such a being, if it existed only in the mind, would be less great than one existing in reality as well. So it must exist in reality. Most philosophers suspect a trick, though they disagree about where it is. Kant's famous objection is that existence is not a property that adds to a concept; a hundred real coins and a hundred imagined ones have the same definition.

The design argument points to order and apparent purpose in nature. William Paley compared the world to a watch found on a heath, whose intricacy implies a maker. David Hume's Dialogues Concerning Natural Religion, published after his death, raised objections that are still discussed: the analogy is weak, and even if it worked it would not establish one good, all-powerful designer.

The problem of evil

The strongest argument against God, for many people, is suffering. If God is all-powerful, all-knowing and wholly good, why is there so much evil? The argument is old; a version is traditionally attributed to Epicurus.

Contemporary philosophers distinguish two forms. The logical form, pressed by J. L. Mackie in 1955, claims that God and evil are flatly inconsistent. Alvin Plantinga's free will defense replied that a world with genuinely free creatures may be better than one without them, and that God could not guarantee that free creatures would always choose well; that possibility is enough to defeat a charge of contradiction. Most philosophers now accept that the logical form fails.

The evidential form, associated with William Rowe, is harder. Rowe asked us to imagine a fawn burned in a forest fire, suffering for days before it dies, unseen by anyone. Grant that such evil is logically compatible with God. Is it not still strong evidence against a good God, since no good seems to require it? Replies include skeptical theism, the view that we are in no position to know what goods an infinite mind might see. Critics worry that this much skepticism undermines other moral judgments too. This debate is live, and no one should tell you it is settled.

Religious experience

Many believers do not hold their faith because of arguments at all. They hold it because of experience. Can experience count as evidence? Al-Ghazālī, in his Deliverance from Error, described turning from philosophy and theology to the Sufi path, where knowledge comes by dhawq, "tasting", rather than by demonstration. William James's The Varieties of Religious Experience (1902) studied mystical states with a psychologist's care and suggested we judge them by their fruits in a life rather than by their roots. Rudolf Otto described the "numinous", an awe unlike any other feeling.

The philosophical question is sharp. If someone tells you they saw a heron, you generally believe them. If they tell you they encountered God, should you treat their report differently, and on what principle?

Beyond one God

Philosophy of religion is not only about the God of Judaism, Christianity and Islam. Buddhist philosophers argued at length against a creator God; the Advaita Vedānta tradition speaks of Brahman, an ultimate reality beyond personal attributes; Daoist texts describe a Way that cannot be named. Comparing these traditions raises its own questions. Are they different routes to one reality, as some pluralists hold, or genuinely different claims, at most one of which can be right? Are mystical experiences across traditions the same experience differently described, as Walter Stace argued, or shaped from the start by the tradition that frames them, as Steven Katz replied?

How to begin

My own conviction, after many years in classrooms, is that philosophy of religion is best done with believers and unbelievers in the same room. Each side sees weaknesses in its own position more clearly when someone who disagrees is there to point them out, and each learns that the other is not stupid.

For a first book, Tim Bayne's Philosophy of Religion: A Very Short Introduction is fair to everyone. Then read Anselm's short argument and Hume's Dialogues side by side. If you want a medieval guide who took both reason and revelation seriously, Maimonides is waiting, and he warned his readers to take their time.