146 How to Win Every Argumentfitness of a candidate for foster-parent, for example, it would be
prudent to make a judgement on the basis of only one previous
incident of child-molesting. In the film Dr Strangelove, when a
psychotic commander sends his wing on a nuclear attack against
the USSR, the General reassures the President: 'You can't con-
demn the whole system just because of one let-down.' Both of
these cases deal with systems which seek 100 per cent safety
coverage, and in which one exception does validate a judge-
ment. Secundum quid covers the more general circumstance in
which it does not.
A visitor who assesses the population of London from his
experience of a royal wedding day is likely to be as wrong as one
who makes a similar judgement about Aberdeen on a charity-
collection day. The basic rule is 'don't jump to conclusions'.
Opinion pollsters try to be very careful to avoid secundum
quids. A famous American poll once wrongly predicted a
Republican victory because it surveyed by telephone, not rea-
lizing that fewer Democrats owned telephones. Political parties
everywhere are not averse to 'talking up' their support by
quoting obviously unrepresentative poll-findings.
Scientific knowledge is like a battlefield mined with secundum
quids. Scientific theories are often put forward with only a very
few examples to back them up. The problem is one of knowing
when there are enough case-histories to be sure about the gen-
eral rule put forward to explain them. Astonishingly, the answer is
never. Science proceeds with the knowledge that a new case
could suddenly appear to show that even its most solid theories
are no good. A billion apples might have hit a billion heads since
Newton's, but it would still take only one apple going upward to
force at least a modification to the general theory.
Secundum quids will be very useful to you in persuading
audiences to pass judgements which coincide with your own.
You should appeal to one or two cases, well-known ones if
possible, as proof of a general judgement.