Lipton responds to the point in a way that may help. I have quoted more thanI would normally but have deleted text where possible and put in bold Lipton's key moves. I have also added 'optional' text in which Lipton deals with potential objections :
I will focus especially on the argument from 'underconsideration'.
This argument has two premises. The ranking premise states that the
testing of theories yields only a comparative warrant.* Scientists can
rank the competing theories they have generated with respect to
likelihood of truth. The premise grants that this process is known to
be highly reliable, so that the more probable theory is always ranked
ahead of a less probable competitor and the truth, if it is among the
theories generated, is likely to be ranked first, but the warrant remains
comparative. In short, testing enables scientists to say which of the
competing theories they have generated is likeliest to be correct, but
does not itself reveal how likely the likeliest theory is. **The second
premise of the argument, the no-privilege premise, states that
scientists have no reason to suppose that the process by which they
generate theories for testing makes it likely that a true theory will be
among those generated. It always remains possible that the truth lies rather among those theories nobody has considered, and there is no
way of judging how likely this is. The conclusion of the argument is
that, while the best of the generated theories may be true, scientists
can never have good reason to believe this. They know which of the
competing theories they have tested is likeliest to be true, but they
have no way of judging the likelihood that any of those theories is
true. On this view, to believe that the best available theory is true
would be rather like believing that Jones will win the Olympics when
all one knows is that he is the fastest miler in Britain.
Let us now consider the argument from underconsideration in its
The most straightforward way to eliminate a gap between comparative and absolute evaluation would be by exhaustion. If the
scientist could generate all possible competitors in the relevant
domain, and he knew this, then he would know that the truth is
among them. Given the reliability that the ranking premise grants,
he would also know that the best of them is probably true. This
brute-force solution, however, seems hopeless, since it takes a
wildly exaggerated view of the scientist's abilities. Even granting
that we can make sense of the notion of all possible competitors,
how could the scientists possibly generate them all?
But collapsing the distinction between relative and absolute
evaluation does not require exhaustion. The scientist does not have
to know that he has considered all the competitors, only that one of
those he has considered must be true, and for this he needs only a
pair of contradictories, not the full set of contraries. It is enough
that the scientist consider a theory and its negation, or the claim that
a theory has a probability greater that one-half and the claim that it
does not, or the claim that X is a cause of some phenomenon and
the claim that it isn't, or the claim that an entity or process with
specified properties exists or it doesn't. Since scientists are plainly
capable of considering contradictories and the ranking premise entails that, when they do, they will be able to determine which is
true, the argument from underconsideration fails.
This is the gist of Lipton's reply. If you want to read beyond this, I include his consideration of two possible replies.
The sceptic has two natural replies to this objection from contradictories. The first is to modify and restrict the ranking premise, so
it concedes only the ability to rank contraries, not contradictories.
But while the original ranking premise is epistemically over-
generous, it is not clearly over-generous in this way. Scientists do,
for example, compare the likelihood of the existence and non-
existence of entities, causes and processes. So the sceptic would
owe us some argument for denying that these comparisons yield
reliable rankings while accepting the reliability of the comparisons
of contraries. Moreover, it is not clear that the sceptic can even
produce a coherent version of this restricted doctrine. The problem
is that a pair of contraries entails a pair of contradictories. To give
a trivial example, (P&Q) and -P are contraries, but the first entails
P, which is the contradictory of -P. Indeed, all pairs of contraries
entail a pair of contradictories, since one member of such a pair
always entails the negation of the other. Suppose then that we wish
to rank the contradictories TI and -Ti. If we find a contrary to TI
(say T2) that is ranked ahead of TI, then -Ti is ranked ahead of
T 1, since T2 entails -T 1. Alternatively, if we find a contrary to -T I
(say T3) that is ranked ahead of -TI, then Ti is ranked ahead of
-T1, since T3 entails TI. So it is not clear how to ban the ranking
of contradictories while allowing the ranking of contraries.
The second natural reply the sceptic might make to the objection
from contradictories would concede contradictory ranking. For in
most cases, only one of a pair of contradictories would mark a
significant scientific discovery. Not to put too fine a point on it,
usually one member of the pair will be interesting, the other boring.
Thus if the pair consists of the claim that all planets move in ellipses
and the claim that some don't, only the former claim is interesting.
Consequently, the sceptic may concede contradictory ranking but
maintain that the result will almost always be that the boring
hypothesis is ranked above the interesting one. In short, he will
claim that the best theory is almost always boring, so the scientist
will almost never be in a position rationally to believe an interesting
This concession substantially changes the character of the
argument from underconsideration, however, and it is a change for the worse. Like most important sceptical arguments, what made the
original argument from underconsideration interesting was the idea
that it might rule out reasons for belief, even in cases where the
belief is in fact true. (Compare Hume's general argument against
induction: he does not argue that the future will not resemble the
past, but that, even if it will, this is unknowable.) With the con-
cession, however, the argument from underconsideration reduces
to the claim that scientists are unlikely to think of the truth. The idea
that scientists are only capable of relative evaluation no longer plays
any role in the argument, since ranking of contradictory theories
has collapsed the distinction between relative and absolute
evaluation, and the argument reduces to the observation that
scientists are unlikely to think of interesting truths, since they are
hidden behind so many interesting falsehoods.
So the revised argument is substantially less interesting than the
original. But the situation is worse than this. For scientists do in fact
often rank interesting claims ahead of their boring contradictories.
The revised argument thus faces a dilemma. If it continues to grant
that scientists are reliable rankers, then the fact that interesting
claims often come out ahead refutes the claim that scientists do not
generate interesting truths. If, on the other hand, reliable ranking is
now denied, we have lost all sense of the original strategy of
showing. how even granting scientists substantial inductive powers
would be insufficient for rational belief.
P. Lipton, 'Is the Best Good Enough?', Proceedings of the Aristotelian Society, New Series, Vol. 93 (1993), pp. 89-104 : 89-96 passim.