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What does he mean by reductionist?
Well "reductionism" is a philosophical model closely related to positivism. It "reduces" all explanations to exclude all conceptual/extra-physical reality causes.
New atheists like Dawkins appear to have been surepticiously pushing this, although without making it explicit because Dawkins knows how much ire it will invite from the scientific community at large (who unlike Bigguns suggested, are not so confident that science dismisses questions of the divine).
Dawkins often appears to imply certain beliefs without making them explicit, which may be why he's often accused of things he hasn't explicitly promoted. What specifically were you alluding to in the interview?