Faith and Reason: Knowledge and dogma and truth: What should we believe? Why? and on what authority? Andrew Brown, our Religious Affairs Correspondent, argues the opposite cases of Sir Karl Popper and the Pope.

POPE JOHN PAUL II's extraordinary publishing success with Crossing the Threshold of Hope draws attention to a huge philosophical divide between Catholics and Anglicans.

In all the fuss about women priests, it is easy to lose sight of the fact that the profoundly important differences between the churches are about authority. The problem is not that they come to different conclusions, but that they reach these differing conclusions by different and largely incompatible routes.

'I think, therefore I am' seems to the Pope to be a disastrous philosophical mistake. 'Descartes . . . turns his back on metaphysics and concentrates on the philosophy of knowledge,' the Pope writes, and he means this as a condemnation.

Crammed into a nutshell, the difference is this: the Pope, and traditionalist forces generally, believe you can have reliable dogma without knowledge, and the rest of the Christian world believes you can have reliable knowledge without dogma.

Perhaps the clearest expression of the anti-papal view was that of the philosopher Karl Popper, who died last month. He had a huge influence on British theologians, though he did not write much on religion directly. But one of his central themes is also central to any philosophy of religion. He is always asking 'What should we believe? Why? and on what authority?'

Much of his influence on theologians came from his destructive work on some of the theories which had competed with Christianity as general explanations for the human predicament, such as Marxism and Freudianism. These had derived their authority less from experience than from the prestige of science, since both claimed to be scientific accounts of the world and of ourselves. Popper gave very good reasons for supposing that such theories were not, and could not be, scientific. They were merely dogmas disguised as knowledge.

Popper believed that objective truth existed and that it could be approached by human reason. But he saw this process as one in which truth was, so to say, the passive partner; whereas, to the Pope, truth reaches out towards humanity.

Scientific enquiry was for him the most clearly defined and self- conscious approach to truth, but it differed only in degree from all other productive exercises of reason. All purposeful behaviour could be understood as implying theories or hypotheses about the outside world. A cat miaows outside the refrigerator, and this action implies in turn a whole set of propositions about tins of cat food, refrigerators, human beings, and ways to bring all these factors into conjunction for the advantage of the cat.

This is an endlessly fascinating and fruitful way to look at the world. When my first child was born, I had been reading little else in English but Popper for about six months, and I watched the child's development keenly for unconscious hypotheses. Sure enough, I could see him testing such ideas as that things exist even when you can't see them; that dropped things fall; that noises affect adults. Each of these ideas was tested against its opposite, and finally adopted. Of course, the process was pre-scientific, and even pre-linguistic. That is why Popper's ideas were so powerful. They offered a very general theory of knowledge and of rationality.

It is this general theory which had a curious influence on the Church of England, one clearly displayed by an obituary in the Church Times by Canon Derek Stanesby, who runs a sort of floating salon for scientists and theologians in a house between the chapel and the walls of Windsor Castle.

The truth, to Popper, is such an overwhelming reality that we can never be sure we have grasped it. We can have good reasons for believing that one idea is closer to truth than another, but we can have no confidence that it is the closest possible.

Canon Stanesby argues, following Popper, that 'Rationality is about making mistakes and learning from them. This is the critical method, and it is the only rational or reasonable way to proceed, whether in science, in politics, or in religion.'

Such a belief about knowledge has profound religious implications, which Canon Stanesby sees and enunciates clearly. 'The doctrines handed down to us by our Christian forebears are not beyond criticism and not necessarily the last word. These doctrines developed by much the same rational process as scientific theories.

'They resulted from centuries of argument and debate, of hard thinking and critical appraisal . . . And just as our knowledge and understanding of the world is fallible, not the last word, or the final truth, so too our knowledge and understanding of God is fallible, not the last word or the absolute truth.'

Against this comes the clarion blast of Pope's rhetoric. 'This world which appears to be a great workshop in which knowledge is developed by man, which appears as progress and civilisation, as a modern system of communications, as a structure of democratic freedoms without any limitations, this world is not capable of making man happy.'

Leaving all questions of truth aside for the moment, it is noteworthy which message the world wants to hear. Dogma sells in millions of copies; Popper in only thousands. It would be impertinent to enquire which of the two more people actually live by.