I often reflect on Cicero's insight here when reading Christopher Hitchens's God is not Great, one of the core texts of the New Atheism. God is Not Great is written with such conviction and confidence that, if self-assurance and conviction were indications of truth, Hitchens would win his arguments hands down.
Furthermore, his assertions seem accepted as oracles of truth by his devotees. Perhaps this helps us understand how the New Atheist notion of faith has achieved such prominence, despite its obvious inaccuracy.
One of the core New Atheist assertions, endlessly and uncritically repeated on New Atheist websites, is Richard Dawkins's dogmatic statement that faith is "blind trust, in the absence of evidence, even in the teeth of evidence."
For Dawkins, this means that faith counts as a "form of mental illness." This nasty intellectual perversion is limited to religious people. "Faith, being belief that isn't based on evidence, is the principal vice of any religion."
Where science and reason prove their convictions, religious people run away from facts and evidence, and live in a fantasy world that is totally disconnected with reality. As Dawkins puts it, "faith is the great cop-out, the great excuse to evade the need to think and evaluate evidence."
It's a familiar slogan. Yet familiarity is not an indicator of truth or reliability. For a start, no Christian theologian I know would accept this notion of faith. It is Dawkins's own invention, designed with his own polemical agendas in mind.
Furthermore, the simple reality of life is that all of us, irrespective of our views about God, base our lives on beliefs - on things that we cannot prove to be true, but believe to be trustworthy and reliable.
The New Atheism seems to have some kind of aversion to using the word "faith," believing it denotes some kind of intellectual perversity reserved for deluded religious fools. Faith, we are told, is invariably blind faith.
I have no doubt that some religious people do have blind faith. Having explored lots of New Atheist websites, I find precisely the same phenomenon exists there as well. It's depressing how a guru-mentality seems to have descended on the movement.
For some New Atheists, the deliverances of superstars such as Dawkins and Hitchens are to be trusted on account of their intergalactic fame. Worried atheists outside the New Atheist bubble are alarmed that personality cults are overtaking this new movement, and that followers are being encouraged simply to echo the views and actions of their gurus.
For example, the secularist group, "Freethinkers" - which is "guided by reason and logic" - has on sale a T-shirt printed with advice on how to tackle life's great ethical questions. Just ask: "What would Dawkins do?" Neat, eh?
So what is faith? Why is belief such a normal and important way of life, whatever the New Atheist establishment says about the matter (and no matter how confidently it says it)?
The simple truth is that belief is just a normal human way of making sense of a complex world. It is not blind - it just tries to make the best sense of things on the basis of the limited evidence available.
As the philosopher Julia Kristeva observed, "whether I belong to a religion, whether I be agnostic or atheist, when I say 'I believe', I mean 'I hold as true'."
Dawkins clearly believes otherwise. He set out his characteristic views on this matter in The Selfish Gene back in 1976.
"[Faith] is a state of mind that leads people to believe something - it doesn't matter what - in the total absence of supporting evidence. If there were good supporting evidence, then faith would be superfluous, for the evidence would compel us to believe it anyway."
This is an unsustainable view of the relation of evidence and belief in the natural sciences, or anywhere else. For a start, it fails to make the critical distinction between the "total absence of supporting evidence" and the "absence of totally supporting evidence." Think about it.
For example, consider the current debate within cosmology over whether the "big bang" gave rise to a single universe, or a series of universes (the so-called "multiverse").
I have many distinguished scientific colleagues who support the former approach, and equally distinguished scientific colleagues who support the latter. Both are real options for thinking and informed scientists, who make their decisions on the basis of their judgements of how best to interpret the evidence.
They believe - but cannot prove - that their interpretation is correct. And nobody thinks they are deluded, mentally ill, or immoral for believing such things.
This doesn't fit at all with Dawkins's bold declaration that "if there were good supporting evidence, then faith would be superfluous, for the evidence would compel us to believe it anyway."
To judge by his comments in The God Delusion, Dawkins himself clearly believes in the "multiverse" theory. But the evidence for it just isn't good enough to compel him - or anyone else - to accept it (or its alternatives).
The great British philosopher and intellectual historian Sir Isaiah Berlin (1909-97) pointed out years ago that human convictions can be grouped together under three categories:
1. Those that can be established by empirical observation;
2. Those that can be established by logical deduction;
3. Those that cannot be proved in either of these ways.
The first two categories concern what can be known reliably through the natural sciences on the one hand, and what can be proved through logic and mathematics on the other.
The third category concerns the values and ideas that have shaped human culture and given human existence direction and purpose - but which cannot be proved by reason or science.
Some examples? It is immoral to rape people. Democracy is better than fascism. World poverty is morally unacceptable. I can't prove any of these beliefs to be true, and neither can anyone else. Happily, that has not stopped moral and social visionaries from acting on their basis, and trying to make the world a better place.
Christopher Hitchens declares boldly that New Atheists such as himself do not hold any beliefs. "Our belief is not a belief." This astonishing statement is one of the best examples of blind faith I have come across - a delusion that makes his whole approach vulnerable.
To give one obvious example: Hitchens's anti-theism rests on certain moral values (such as "religion is evil" or "God is not good") which he is unable to demonstrate by reason.
Hitchens simply assumes that his moral values are shared by his sympathetic readers, who are unlikely to ask inconvenient questions about their origins, foundations or reliability.
When he is called upon to prove them - as he regularly is in debates - he seems unable to do so. His beliefs are indeed beliefs, even if he prefers not to concede this decisive point.
Welcome to the human race, Mr Hitchens. That's the position we're all in - including you.
But what of a specifically religious faith? Christians believe that certain things are true, that they may be relied upon, and that they illuminate our perceptions, decisions and actions. Faith enables us to see things in different ways, and thus leads us to act in ways consistent with this.
As William James pointed out many years ago, religious faith is basically "faith in the existence of an unseen order of some kind in which the riddles of the natural order may be found and explained." Faith is based on reason, yet not limited to the somewhat meagre truths that reason can actually prove.
So is this irrational, as the New Atheist orthodoxy declares? Christianity holds that faith is basically warranted belief. Faith goes beyond what is logically demonstrable, yet is nevertheless capable of rational motivation and foundation.
It is not a blind leap into the dark, but a joyful discovery of a bigger picture of things, of which we are part. It is complex and rich idea, which goes far beyond simply asserting or holding that certain things are true.
It is a relational idea, pointing to the capacity of God to captivate our imaginations, and to accompany us on the journey of life.
Such statements will raise questions for readers, not least concerning the realms of reason and science, so highly cherished by the New Atheism. I cherish them too, as do most Christians. But they don't take us where the New Atheism seems to think they do, as we shall see in my next article.
Alister McGrath, a former atheist, is Professor of Theology, Ministry, and Education at King's College, London. His book "Why God won't go away" will be published by SPCK in February 2011, and by Thomas Nelson in May 2011.