  Following Pollock (1986), we can distinguish between undercutting and rebutting defeaters. Intuitively, where E is evidence for H, an undercutting defeater is evidence which undermines the evidential connection between E and H. Thus, evidence which suggests that you are a pathological liar constitutes an undercutting defeater for your testimony: although your testimony would ordinarily afford excellent reason for me to believe that your name is Fritz, evidence that you are a pathological liar tends to sever the evidential connection between your testimony and that to which you testify. In contrast, a rebutting defeater is evidence which prevents E from justifying belief in H by supporting not-H in a more direct way. Thus, credible testimony from another source that your name is not Fritz but rather Leopold constitutes a rebutting defeater for your original testimony. It is something of an open question how deeply the distinction between ‘undermining’ and ‘rebutting’ defeaters cuts.