The most famous description of faith comes in the anonymous New Testament epistle to the Hebrews: “Now faith is the substance of things hoped for, the evidence of things not seen.”
Interestingly, faith is linked with evidence, and is indeed here seen as a form of evidence. In many exchanges with atheists over the years, I have been told that faith is irrational and therefore delusional, in contrast with their stance, which they say is clear-sighted and rational.
It seems to me that such a belief requires an entirely uncritical faith, combined with a lack of self-knowledge. 
For if one thing is clear in the 21st century, it is that we are not transparent to ourselves, especially when we think we are. David Hume, the 18th century philosopher, observed with some justice that reason is – and ought to be – the slave of our passions.
We think we are employing unalloyed reason but often little understand how much it is shaped by our preferences, prejudices or unconscious influences of which we are unaware. Often what we regard as reason is much adulterated by its near-cousin, rationalisation. We use reason to justify a position or decision we have already taken – or, to put it more poetically as Blaise Pascal did, “the heart has its reasons which reason does not know”.
In fact, faith and reason are not polar opposites, as my atheist friends often aver, but exist on a continuum and can overlap and reinforce each other.
Sometimes we may trust one person but not another without being able to explain precisely why. It is a combination of reason – judging argument, motive, demeanour and so on – and non-rational but real perceptions of body language, and doubtless many more factors. But it is perfectly reasonable – in the sense that anyone can understand it – to speak of having faith in someone we trust.
Indeed, our daily lives could not operate if we never employed faith but acted on the basis of sceptical philosophy. We don't know that the next tram will arrive, but we believe it will, and the fact that we are sometimes wrong does not disturb that faith.
We operate with the best knowledge available, often including faith. We spend decades investing in superannuation built partly on the premise that the sharemarket rises over time, despite oscillations.
That belief is based on history, analysis and wide knowledge, but also no small modicum of faith. And, thus far, it has worked. When market experts talk of the confidence necessary for people to invest and for growth to happen, they are really talking of faith.
For the religious believer, faith combines many of these same properties: analysis, experience, the promptings of the heart. That is no guarantee it is justified, but none of us operates on the basis of guarantees.
Barney Zwartz is a Senior Fellow with the Centre for Public Christianity.
This article first appeared in The Age.
