The runaway train 143
your required destination you cannot leave it, but are compelled
to be taken further than you wished. The runaway-train fallacy is
committed when an argument used to support a course of action
would also support more of it. If you wish to stop at a particular
point, you need an argument to do so.
It might well be true that lowering a highway speed-limit from
70 mph to 60 mph would save lives. That is not a sufficient
argument for choosing 60 mph, however, because lowering the
speed-limit to 50 mph would save even more lives. And more still
would be saved at 40 mph. The obvious conclusion of this run-
away train is that if saving lives is the sole aim, the speed-limit
should be set at the level which saves the most, and this is 0 mph.
In practice the lives at risk for each proposed speed-limit have
to be measured against what is achieved by the ability to travel
and to transport goods rapidly. Most of our daily activities
involve a degree of risk which could be reduced if we limited our
actions. In practice we trade off risks against convenience and
comfort. If the case for making the speed-limit 60 mph is based
solely on the lives which could be saved, the arguer will need
additional reasons to stop at 60 mph before the runaway train of
his own argument takes him to 50 mph, then 40 mph, and
finally crashes into the buffers when it reaches 0 mph.
People argue that since, in the UK, everyone has to pay for the
country's National Health Service, this gives the state a sufficient
justification to ban smoking, because smokers suffer more ill-
nesses. There may be good reasons to ban smoking, but the
argument that the costs of the smoker's behaviour should be
imposed on others is a runaway train. Why stop there? The same
argument applies to all behaviour which affects health adversely.
It could be applied to the eating of saturated fats such as butter,
or refined white sugar. The state could require people to exercise
in order to prevent the health costs of their laziness from falling
on others. If this argument is to apply only to smoking, there
have to be reasons why the train stops there.