For example, The Pook's assertion that William James's comment is only true if God exists has as an unstated premise that a man has a true existence only if there is God to perceive that true existence. The assertion was worded in such a way as to appear to be a proof of the existence of God. Hence my claim of petitio principii. But perhaps The Pook was offering it as a reductio ad absurdum. One never know, do one?