“'do not pretend that conclusions are certain which are not demonstrated or demonstrable: Such was the principle of 'agnosticism', a word that Huxley had come up with himself and which he cast as the essential requirement for anyone who wished to practise science. It was, he flatly declared, ‘the only method by which truth could be ascertained’. Everyone reading him knew his target. Truth that could be neither demonstrated nor proven, truth that was dependent for its claims on a purportedly supernatural revelation, was not truth at all. Science as a practitioner of the fashionable new art of photography might have put it-was defined by its negative: religion.”