 Laudan is certainly right to distinguish these various versions of holist underdetermination, and he is equally right to suggest that many of the thinkers he confronts have derived grand morals concerning the scientific enterprise from much stronger versions of underdetermination than they are able to defend, but the underlying situation is somewhat more complex than he suggests. Laudan’s overarching claim is that champions of holist underdetermination show only that a wide variety of responses to disconfirming evidence are logically possible (or even just psychologically possible), rather than that these are all rationally defensible or equally well-supported by the evidence. But his straightforward appeal to further epistemic resources like ampliative principles of belief revision that are supposed to help narrow the merely logical possibilities down to those which are reasonable or rationally defensible is itself problematic, at least as part of any attempt to respond to Quine. This is because on Quine’s holist picture of knowledge such further ampliative principles governing legitimate belief revision are, of course, themselves simply part of the web of our beliefs, and are therefore open to revision in response to recalcitrant experience as well—indeed, this is true even for the principles of deductive logic and the (consequent) demand for particular forms of logical consistency between parts of the web itself! So while it is true that the ampliative principles we currently embrace do not leave all logically or even psychologically possible responses to the evidence open to us (or leave us free to preserve any hypothesis “come what may”), our continued adherence to these very principles, rather than being willing to revise the web of belief so as to abandon them, is part of the phenomenon to which Quine is using underdetermination to draw our attention and cannot be taken for granted without begging the question. Put another way, Quine does not simply ignore the further principles that function to ensure that we revise the web of belief in one way rather than others, but it follows from his account that such principles are themselves part of the web and therefore candidates for revision in our efforts to bring the web of beliefs into conformity (by the resulting web’s own lights) with sensory experience. This recognition makes clear why it will be extremely difficult to say how the shift to an alternative web of belief (with alternative ampliative or even deductive principles of belief revision) should or even can be evaluated for its rational defensibility—each proposed revision will be maximally rational by the lights of the principles it itself  sanctions.[5]  Of course we can rightly say that many candidate revisions would violate our presently accepted ampliative principles of rational belief revision, but the preference we have for those rather than the alternatives is itself a matter of their position in the existing web of belief we have inherited and the role that they themselves play in guiding the revisions we are inclined to make to that web in light of ongoing experience.