Evaluation of Example 1: Phytochemicals

Passage:

“Scientists have discovered the reason why plant foods offer such powerful cancer protection. Certain substances found only in plant foods are known collectively as phytonutrients (phyto is a Greek word meaning ‘plant’) have the ability to stop cancer.”

Selene Yeager, et al. The Doctors Book of Healing Foods (Emmaus, Pennsylvania: Rodale Inc., 2008), 21.

Analsyis:

The passage commits the petitio principii informal fallacy. Essentially the argument is that some plants when eaten offer cancer protection because of their cancer-fighting properties. ‘Phytonutrient’ is a term used in the manner of what Jeremy Bentham refers to as a question-begging epithet.