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Author Information: Robin McKenna, University of Liverpool,

McKenna, Robin. “McBride on Knowledge and Justification.” Social Epistemology Review and Reply Collective 7, no. 9 (2018): 53-59.

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I would like to thank the editors of the Social Epistemology Review and Reply Collective for giving me the opportunity to review Mark McBride’s rich and rewarding book. To begin, I will give a—fairly high-level—overview of its contents. I will then raise some concerns and make some (mildly) critical comments.


The book is split into two parts. Part 1 concerns the issue of basic knowledge (and justification), whereas the second concerns (putative necessary) conditions on knowledge (specifically, conclusive reasons, sensitivity and safety conditions). We can start with Part 1. As McBride defines it, basic knowledge is “knowledge (or justification) which is immediate, in the sense that one’s justification for the known proposition doesn’t rest on any justification for believing other propositions” (p. 1).

Two central issues in Part 1 are (i) what, exactly, is wrong with Moore’s “proof” of the external world (Chapter 1) (ii) what, exactly, is wrong with inferences that yield “easy knowledge” (Chapters 2-3). Take these arguments, which for ease of reference I’ll call MOORE and EASY-K respectively:


(Visual appearance as of having hands).
1-M. I have hands.
2-M. If I have hands, an external world exists.
3-M. An external world exists.


(Visual appearance as of a red table).
1-EK. The table is red.
2-EK. If the table is red, then it is not white with red lights shining on it.
3-EK. The table is not white with red lights shining on it.

It seems like a visual appearance as of having hands can give one knowledge of 1-M, and 2-M seems to be knowable a priori. But it seems wrong to hold that one can thereby come to know 3-M. (And mutatis mutandis for EASY-K and 3-EK).

I want to single out three of McBride’s claims about MOORE and EASY-K. First, it is commonly taken that “dogmatist” responses to MOORE (such as Pryor 2000) are at a disadvantage with respect to “conservative” responses (such as Wright 2004). The dogmatist holds that having a visual appearance as of hands provides immediate warrant for 1-M, whereas the conservative holds that one can have warrant for 1-M only if one has a prior entitlement to accept 3-M. Thus the dogmatist seems forced to accept that warrant can “transmit” from the premises of MOORE to the conclusion, whereas the conservative can deny that warrant transmission occurs.

In Chapter 1 McBride turns this on its head. First, he argues that, while a conservative such as Crispin Wright can maintain that the premises of MOORE don’t transmit “non-evidential” warrant to the conclusion, he must allow that “evidential” warrant does transmit from the premises to the conclusion. Second, he argues that Wright cannot avail himself of what McBride (following Davies 2004) takes to be a promising diagnosis of the real problem with MOORE. According to Martin Davies, MOORE is inadequate because it is of no use in the epistemic project of settling the question whether the external world exists. But, for Wright, there can be no such project, because the proposition that the external world exists is the “cornerstone” on which all epistemic projects are built.

Second, in Chapter 3 McBride seeks to show that the dogmatist can supplement Davies’ account of the problem with Moore’s proof in order to diagnose the problem with EASY-K. According to McBride, EASY-K is problematic not just in that it is of no use in settling the question whether the table is not white with red lights shining on it, but also in that there are all sorts of ways in which one could settle this question (e.g. by investigating the lighting sources surrounding the table thoroughly).

Thus, EASY-K is problematic in a way that MOORE isn’t: while one could avail oneself of a better argument for the conclusion of EASY-K, it is harder to see what sort of argument could improve on MOORE.

Third, while Part 1 is generally sympathetic to the dogmatist position, Chapter 5 argues that the dogmatist faces a more serious problem. The reader interested in the details of the argument should consult Chapter 5. Here, I just try to explain the gist. Say you endorse a closure principle on knowledge like this:

CLOSURE: Necessarily, if S knows p, competently deduces q from p, and thereby comes to believe q, while retaining knowledge of p throughout, then S knows q (p. 159).

It follows that, if one comes to know 1-EK (the table is red) by having an appearance as of a red table, then competently deduces 3-EK (the table is not white with red lights shining on it) from 1-EK while retaining knowledge of 1-EK, then one knows 3-EK. But—counter-intuitively—having an appearance as of a red table can lower the credence one ought to have in 3-EK (see pp. 119-20 for the reason why).

It therefore seems inarguable that, if you are in a position to know 3-EK after having the appearance, you must have been in a position to know the 3-EK prior to the appearance. So it seems like the conservative position must be right after all. In order for your appearance as of a red table to furnish knowledge that there is a red table you must have been in a position to know that the table was not white with red lights shining on it prior to having the appearance as of a red table.

The second part of McBride’s book concerns putative (necessary) conditions on knowledge, in particular conclusive reasons (Chapter 6), sensitivity (Chapter 7) and safety (Chapter 8). McBride dedicates a chapter to each condition; the book finishes with a (brief) application of safety to legal knowledge (Chapter 9). While most epistemologists tend to argue that either sensitivity or (exclusive) safety are a (necessary) condition on knowledge, McBride provides a (qualified) defense of both.

In the case of sensitivity, this is in part because, if sensitivity were a condition on knowledge, then—as Nozick (1981) famously held—CLOSURE would be false, and so the argument against dogmatism (about knowledge) in Chapter 5 would be disarmed. Because of the centrality of sensitivity to the argument in Part 1, and because the chapters on conclusive reasons and sensitivity revolve around similar issues, I focus on sensitivity in what follows.

Here is an initial statement of sensitivity:

SENSITIVITY: S knows p only if S sensitively believes p, where S sensitively believes p just in case, were p false, S would not believe p (p. 160).

Chapter 7 (on sensitivity) is largely concerned with rebutting an objection from John Hawthorne (2004) to the effect that the sensitivity theorist must also reject these two principles:

EQUIVALENCE: If you know a priori that p and q are equivalent and you know p, then you are in a position to know q.

DISTRIBUTION: If one knows p and q, then one is in a position to know p and to know q.

Suppose I have an appearance as of a zebra. So I know:

(1) That is a zebra.

By EQUIVALENCE I can know:

(2) That is a zebra and that is not a cleverly disguised mule.

So by DISTRIBUTION I can know:

(3) That is not a cleverly disguised mule.

But, by SENSITIVITY, while I can know (1), I can’t know (3) because, if I were looking at a cleverly disguised mule, I would still believe I was looking at a zebra. Hawthorne concludes that the sensitivity theorist must deny a range of plausible principles, not just CLOSURE.

McBride’s basic response is that, while SENSITIVITY is problematic as stated, it can be modified in such a way that the sensitivity-theorist can deny EQUIVALENCE but keep DISTRIBUTION. More importantly, this rejection of EQUIVALENCE can be motivated on the grounds that initially motivate SENSITIVITY. Put roughly, the idea is that simple conjunctions like (4) already cause problems for SENSITIVITY:

(4) I have a headache and I have all my limbs.

Imagine you form the belief in (4) purely from your evidence of having a headache (and don’t worry about how this might be possible). While you clearly don’t know (4), your belief does satisfy SENSITIVITY, because, if (4) were false, you wouldn’t still believe it (if you didn’t have a headache, you wouldn’t believe you did, and so you wouldn’t believe (4)).

The underlying problem is that SENSITIVITY tells you to go the nearest possible world in which the relevant belief is false and asks what you believe there, but a conjunctive belief is false so long as one of the conjuncts is false, and it might be that one of the conjuncts is false in a nearby possible world, whereas the other is false in a more distant possible world. So the sensitivity theorist needs to restrict SENSITIVITY to atomic propositions and add a new condition for conjunctive propositions:

SENSITIVITY*: If p is a conjunctive proposition, S knows p only if S believes each of the conjuncts of p sensitively (p. 167).

If we make this modification, the sensitivity theorist now has an independent reason to reject EQUIVALENCE, but is free to accept DISTRIBUTION.

Critical Discussion

While this only touches on the wealth of topics discussed in McBride’s book, I will now move on to the critical discussion. I will start by registering two general issues about the book. I will then develop two criticisms in a little more length, one for each part of the book.

First, while the book makes compelling reading for those already versed in the literatures on transmission failure, easy knowledge and modal conditions on knowledge, the central problematics are rarely motivated at any length. Moreover, while McBride does draw numerous (substantive) connections between the chapters, the book lacks a unifying thesis. All this to say: This is maybe more of a book for the expert than the novice. But the expert will find a wealth of interesting material to chew over.

Second, readers of the Collective might find the individualism of McBride’s approach striking. McBride is almost exclusively concerned with the epistemic statuses of individuals’ beliefs, where those beliefs are formed through simple processes like perception and logical inference. The one part of the book that does gesture in a more social direction (McBride’s discussion of epistemic projects, and the dialectical contexts in which they are carried out) is suggestive, but isn’t developed in much detail.

Turning now to more substantive criticisms, in Part 1 McBride leans heavily on Davies’ solution to the problem with MOORE. I want to make two comments here. First, it is natural to interpret Davies’ solution as an inchoate form of contextualism (DeRose 1995; Lewis 1996): whether MOORE (and EASY-K?) transmits warrant to its conclusion depends on the context in which one runs the inference, in particular, the project in which one is engaged.

This raises a host of questions. For example: does McBride hold that, if we keep the context (project) fixed, no transmission failure occurs? That is: if we’re working with the (easier) project of deciding what to believe, does an instance of MOORE transmit warrant from premises to conclusion? If so, then if we’re working with the (harder) project of settling the question, does an instance of MOORE fail to transmit warrant? (This would fit with the more general contextualist line in response to the skeptical problem, so this is only a request for clarification).

Second, and more importantly, we need to distinguish between the project of fully settling the question whether p and the project of partially settling the question whether p. Let’s grant McBride (and Davies) that someone who runs through an instance of MOORE has not fully settled the question whether there is an external world. But why think that—at least by the dogmatist’s lights—they haven’t partially settled the question? If dogmatism is true, then having the appearance as of a hand provides immediate warrant for believing that one has a hand, and so, via MOORE, for believing that there is an external world.

McBride (like many others) finds this conclusion unpalatable, and he invokes the distinction between the project of deciding what to believe and the project of settling the question in order to avoid it. But this distinction is overly simplistic. We can settle questions for different purposes, and with different degrees of stability (cf. “the matter is settled for all practical purposes”). The dogmatist seems forced to allow that MOORE is perfectly good for settling the question of whether there is an external world for a range of projects, not just one.

(I have a parallel worry about the solution to the problem of easy knowledge. Let’s grant McBride that one problem with EASY-K is that there are far better ways of trying to establish that the table is not white but bathed in red light. But why think that—at least by the dogmatist’s lights—it isn’t a way of trying to establish this? To point out that there are better ways of establishing a conclusion is not yet to show that this particular way is no way at all of establishing the conclusion).

Finally, in his response to Hawthorne’s objection to the sensitivity theorist McBride is at pains to show that his modification of SENSITIVITY isn’t ad hoc. To my mind, he does an excellent job of showing that the sensitivity theorist should reject EQUIVALENCE for reasons entirely independent of Hawthorne’s objection.

This suggests (at least to me) that the problem is not one of ad hocness, but rather that sensitivity theorists are forced to endorse a wide range of what Keith DeRose (1995) calls “abominable conjunctions” (cf. “I know that I have hands, but I don’t know that I’m not a handless brain in a vat”). DeRose’s own response to this problem is to embed something like SENSITIVITY in a contextualist theory of knowledge attributions. DeRose proposes the following “rule”:

Rule of Sensitivity: When it’s asserted that S knows (or doesn’t know) p, then, if necessary, enlarge the sphere of epistemically relevant worlds so that it at includes the closest worlds in which p is false (cf 1995, 37).

His idea is that, when the question of whether S knows p becomes a topic of conversation, we expand the range of worlds in which S’s belief must be sensitive. Imagine I assert “I know that I have hands”. In order for this assertion to be true, it must be the case that, if I didn’t have hands, I wouldn’t believe that I did.

But now imagine I assert “I know that I’m not a handless brain in a vat”. In order for this new assertion to be true, it must be the case that, if I were a handless brain in a vat, I wouldn’t believe that I wasn’t. Plausibly, this will not be the case, so I can’t truly assert “I know that I’m not a handless brain in a vat”. But no abominable conjunction results, because I can no longer truly assert “I know that I have hands” either.

My suggestion is that, if McBride were to adopt DeRose’s contextualist machinery, he would not only have a way of responding to the problem of abominable conjunctions, but also an interesting modification to DeRose’s “rule of sensitivity”.

For note that DeRose’s rule seems subject to the same problem McBride sees with SENSITIVITY: when I assert “I have a headache and I have all my limbs” we only need to expand the range of worlds to include worlds in which I don’t have a headache, and so my assertion will remain true in the updated context created by my assertion. Further, adopting this suggestion would furnish another link between Part 1 and Part 2: solving the problem of basic knowledge and formulating a satisfactory sensitivity condition both require adopting a contextualist theory of knowledge attributions.

Contact details:


Davies, Martin. 2004. ‘Epistemic Entitlement, Warrant Transmission and Easy Knowledge’. Aristotelian Society Supplementary Volume 78 (1): 213–245.

DeRose, Keith. 1995. ‘Solving the Skeptical Problem’. Philosophical Review 104 (1): 1–52.

Hawthorne, John. 2004. Knowledge and Lotteries. Oxford University Press.

Lewis, David. 1996. ‘Elusive Knowledge’. Australasian Journal of Philosophy 74 (4): 549–67.

Nozick, Robert. 1981. Philosophical Explanations. Harvard University Press.

Pryor, James. 2000. ‘The Skeptic and the Dogmatist’. Noûs 34 (4): 517–549.

Wright, Crispin. 2004. ‘Warrant for Nothing (and Foundations for Free)?’ Aristotelian Society Supplementary Volume 78 (1): 167–212.

Author Information: David Pauleen, Massey University,; David Rooney, Macquarie University, and Ali Intezari, Massey University, A.

Pauleen, David, David Rooney and Ali Intezari. “Big Data, Little Wisdom: Trouble Brewing? Ethical Implications for the Information Systems Discipline.” Social Epistemology Review and Reply Collective 4, no. 8 (2015): 9-33.

The PDF of the article gives specific page numbers. Shortlink:


Image credit: A. Golden, via flickr


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