Reduction and Elimination in Philosophy and the Sciences

could then deduce (1c) and conclude that S does not know
any ordinary proposition p. In another context, different HP
might be taken for granted that are consistent with K(S, p)
but not with some of the sceptic’s presuppositions outlined
above. Then (1) would allow us to infer that S knows the
denial of the sceptical hypothesis. Note, however, that
even if the sceptic relies on certain HP this is not enough
to give a direct argument against her. But it is enough to
restrict the devastating impact on our ordinary knowledge
claims to contexts in which sceptical HP hold. This is one
way to make sense of the conjecture that the truth of a
given knowledge claim can vary with context.
A point that needs more work is avoiding the
account to over generate. So far it seems as if any
knowledge claim could be justified, given that certain HP
hold, as absurd as they may be. So we need a mechanism
that i) restricts the admissible HP and that ii) can bridge
the gap between internal factors like taking something for
granted and the external factors that allow for the
implication K(S, p) → p, i. e., the factivity of knowledge. An
additional externalist conception of justification could solve
both of these problems. Consider, for the sake of
illustration, a reliabilist account that incorporates the
methods by which we form our beliefs about certain
propositions. This would avoid not only fancyful HP as
these would be analogous to unreliable methods, but also
Gettier cases. It would have the further merit of allowing for
fallibility, as a method of forming beliefs that we thought
trustworthy might turn out to be false. In the spirit of the
experiment-example in § 2: Future investigation might
reveal that the apparatus we used is not as precise as we
took it to be or even that it does not measure what we
thought it did. Even though some of the beliefs we based
on the data the apparatus delivered were in fact true, we
would no longer consider them as known due to the
unreliable process by which we formed our belief in them.
However, nothing hinges on this specific epistemological
account. The notion of HP is fairly neutral to other
externalist suggestions.
4. Conversational mechanisms
The analysis sketched so far did not address the conversational
application of different HP. One possibility to systematize
the account seems to be the incorporation of a
Stalnaker-style notion of common ground. The definition is
as follows:
Scepticism, Wittgenstein's Hinge Propositions, and Common Ground — Erik Stei
“It is common ground that Φ in a group if all members
accept (for the purpose of the conversation)
that Φ, and all believe that all accept that Φ, and all
believe that all believe that all accept that Φ, etc.”
(Stalnaker 2002: 716)
Acceptance, following Stalnaker, is a propositional attitude
as well as a methodological stance toward a proposition.
To accept some proposition Φ is to treat it as true and to
“ignore, at least temporarily, and perhaps in a limited context,
the possibility that it is false” (Stalnaker 2002: 716).
Applying this idea to the position developed in § 3, this
means, roughly, that we accept some proposition Φ as true
in a context C1 in order to undertake a reasonable investigation
I1. Given Φ is an essential presupposition in C1,
then in case we doubt Φ, this shifts the context as well as
the investigation we are interested in to I2 in C2. 4 Thus,
4 Stalnaker does not mention context shifts, but only context changes, that
decrease the set of possible worlds under consideration. I distinguish context-
what depends on contextual factors is the question which
propositions we are willing to accept as given and thus
where to stop the regress of justification. The connection I
propose is that HP determine, at least in part, which
propositions we are willing to accept.
In standard cases, conversational contexts are
dynamic in such a way that they are constantly extended
by the incorporation of new information—this is a central
feature of communication and not an instance of context
shifts. It is captured by the notion of accommodation,
which can be illustrated by the following example. Imagine
a conversation between Alice and Bob, where Alice utters:
(2) I can’t come to the meeting – I have to pick up
my sister at the airport.
Given that Alice is a competent speaker of English and
also that the basic pragmatic mechanisms, e. g., a
Gricean-style Cooperative Principle and some conversational
maxims (Grice 1989), are at work, Bob can infer
from (2) that Alice believes that it is common belief that
she has a sister. The latter now common belief (as Bob
believes it as well after Alice’s utterance of (2)) leads Bob
to belief that Alice has a sister, which makes Alice’s having
a sister common belief in the context at issue (cf. Stalnaker
2002: 709-710). If Bob and Alice are discussing the question
who is going to the meeting next Friday, Alice has
merely introduced a proposition to be integrated into the
common ground by decreasing the set of possible world
compatible with the state of the conversation. Consider, in
contrast, the following dialogue:
(3) a. [Alice]: I can’t come to the meeting – I have
to pick up my sister at the airport.
b. [Bob]: You can’t pick up your sister at the
airport. In fact there is no airport, there is no
sister, and I’m not here either. You are a brain
in a vat with all your impressions stimulated by
a mad scientist.
In this case, it does not seem as if Bob introduced new
information. Rather, his answer (3b) reveals a defective
context. While in a nondefective context “the participants’
beliefs about the common ground are all correct” (Stalnaker
2002: 717), this is not the case in a defective context.
Before Bob’s utterance of (3b), Alice believed that a
proposition like that the external world exists was part of
the common ground. Bob’s answer, however, made it
manifest that it was not and thus, that the context was
defective. Alice now seems to have two options: either she
accommodates Bob’s utterance and thus accepts the shift
to a sceptical context, i. e., she accepts entering a new
conversation, or she rejects the context-shift by refusing to
accommodate (3b). This leads to the quite natural result
that in case she accepts the context-shift, we would not be
inclined to ascribe her knowledge of any ordinary proposition.
If, however, she refuses accommodating (3b) we are
still willing to ascribe her knowledge of that proposition. I
think it is the latter option that is more likely to be chosen in
every-day conversation.
shifts as the result of a defective context in which a given conversational aim
could not be achieved. It is similar to beginning an entirely new conversation.
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