Whether God exists or not is one of the most important philosophical questions there is. And the tradition of trying to establish God’s existence involving evidence is a long one, with a golden age during the 17th and 18th centuries – the early modern period.

Attempts to prove God’s existence continue today. But they are on nothing like the same scale as they were hundreds of years ago, with secularism now being as common among philosophers as it is among the general population. And this is not the only difference to have occurred since that golden age, which is the focus of my new book, Proofs of God in Early Modern Europe. Here are three other things that have changed over the centuries:

Aims

When contemporary thinkers try to prove God’s existence, their aim is usually to show that it is in fact reasonable to believe in God. For example, in New Proofs for the Existence of God, Robert J Spitzer advances a series of proofs that together constitute evidence “capable of grounding reasonable and responsible belief in a super-intelligent, transcendent, creative power”.

Such an aim would have struck early modern philosophers as odd, because back then the default view was that belief in God was perfectly reasonable. Indeed, in early modern times, religious belief was so widespread in Europe that the idea of someone sincerely denying God’s existence was often considered to be absurd – if not unthinkable.

So why did early modern philosophers feel the need to construct proofs for something that was already widely believed to be true? Often, they sought to prove God’s existence because of the central explanatory or theoretical role that God played in their philosophical thought.

René Descartes (1596-1650) famously claimed that proving the existence of a perfect God was the only way he could be certain of the reality of the external world. He held that what appeared to him to be true really was true, since it was beyond doubt that a perfect God would not engage in deception or give him senses that were unreliable.

For Baruch Spinoza (1632-1677), establishing whether there is a God had important repercussions not just for what we can know about the world, but also about how we should live. He believed the greatest possible contentment we can experience in this life comes from our knowledge of the essence of things – which in turn comes from understanding God’s attributes. The more we understand things this way, the less troubled we will be by strong emotions and the less we will fear death. For the great thinkers of early modernity, then, establishing God’s existence was of paramount importance.

Confidence

Another big difference between early modern philosophers and those of today is their confidence in the proofs they put forward. Even the most self-assured of contemporary philosophers are likely to claim that their arguments only make God’s existence probable. For example, in The Existence of God, Richard Swinburne offers a variety of proofs that he takes together to show that God’s existence is more probable than not.

Such a claim would have appeared tame to early modern thinkers, who invariably saw their own proofs as capable of establishing God’s existence beyond all reasonable doubt – or even of demonstrating it. Indeed, some thinkers, like John Locke (1632-1704), took their proofs to be on a par with mathematical demonstrations, such that anyone who encountered the proofs could not fail to be convinced by them, so long as his or her rational faculties were intact.

Opponents

But perhaps the biggest difference between contemporary and early modern attempts to prove God’s existence lies in the source of the opposition to these proofs. Many of those who oppose efforts to prove God’s existence today are either atheists, who claim there is no God, or agnostics, who are neutral as to whether there is a God or not. Both atheists and agnostics have a vested interest in undermining proofs for the existence of God.

In the 17th and 18th centuries, however, atheists and agnostics were rare (some even say non-existent for much of that time), and those that were around tended not to be very vocal.

Yet this did not mean that proofs for God’s existence went unopposed. Early modern thinkers were trained in disputation and the practice of tackling objections to their own views. If there weren’t any real opponents to their views, then they were encouraged to invent them, and come up with objections that these imaginary opponents might make.

Some, like Voltaire (1694-1778), got so carried away with this that they spent much more time considering objections to their proofs than they did outlining the proofs themselves. The whole point of the exercise was that theists could then refute all possible objections – and put their view on a firmer footing.

While such a practice may make good academic sense, it did have one unforeseen consequence. The sophisticated objections that early modern theists raised against their own proofs and those of their contemporaries ended up being adopted by later atheist thinkers, who developed and strengthened these objections in an effort to put atheism on a firm rational footing.

So, by concocting objections to their own proofs, early modern philosophers inadvertently helped to fuel the subsequent rise of atheism – by making it a more intellectually respectable position.