 John L. Pollock developed Chisholm’s idea into a theory of prima facie reasons and defeaters of those reasons (Pollock 1967, 1970, 1974, 1987, 1995, 2010). Pollock distinguished between two kinds of defeaters of a defeasible inference: rebutting defeaters (which give one a prima facie reason for believing the denial of the original conclusion) and  undercutting defeaters  (which give one a reason for doubting that the usual relationship between the premises and the conclusion hold in the given case). According to Pollock, a conclusion is warranted, given all of one’s evidence, if it is supported by an ultimately undefeated argument whose premises are drawn from that evidence.