"As yet another (British) panel concluded this week, there is no evidence
that GM crops now in commercial cultivation are more dangerous to human health
than conventional foods. So there is no reason why Europeans should not eat
the GM food that Americans already consume by the siloful."
Economist leader, 26 July 2003

For the critical thinker, no error is more basic than the non sequitur: the
conclusion that doesn’t follow. Non sequiturs are extremely common. People seem
to like to scatter their texts with words like "therefore" and "so"
whether or not the various points they are making in some way follow from each
other.

Saddam Hussain showed himself to be a brilliant exponent of the non sequitur
in his surreal
interview with British parliamentarian Tony Benn. In this short exchange
he used the word "therefore" six times, in every case either creating
a non sequitur or drawing a self-evident conclusion ("Therefore we are
facing a critical situation.") Here’s the best example:

"Those people and others have been telling the various US administrations,
especially the current one, that if you want to control the world you need to
control the oil. Therefore the destruction of Iraq is a pre-requisite to controlling
oil."

The important thing to note about non sequiturs is that what is at issue is
not necessarily the truth of the main claims being made, but the inferential
connection between them. For example, if I say, "I like cheese therefore
it’s Tuesday", I have uttered a non sequitur, since the fact that it is
Tuesday doesn’t follow from the fact that I like cheese. But it may nevertheless
be true both that it is Tuesday and I do like cheese. So the fact that Saddam
uttered a non sequitur does not in itself prove that the US does not want to
control the world’s oil, nor that they didn’t see the destruction of Iraq as
a means of achieving their goal. The complaint about the non sequitur simply
draws our attention to the fact that the need to attack Iraq does not necessarily
follow from the desire to control the world’s oil.

The Economist leader also seems to contain a glaring non sequitur. It
does not follow from the fact that a British panel has concluded that GM foods
are safe to eat that they are actually safe to eat. It may be that insufficient
studies have been conducted to allow us to conclude that absence of evidence
for health risks is evidence for their absence. (See previous bad move, absence
and evidence.)

But here we must be careful not to read such texts as though there were formal
arguments with clearly defined premises and conclusions. The fact is that in
real life not every stage of an argument is usually spelled out. Most arguments
are enthymemes – they rest on unstated, often assumed, premises.

It doesn’t take too much digging to identify the enthymematic nature of the
Economist leader. The first words – "As yet another (British) panel
concluded" suggest that we should assume the premise that there has been
plenty of research into the health risks of GM food, enough to draw a conclusion
from, and that all this research points the same way.

Similarly, the conclusion leaves a little out. When it talks about "no
reason why Europeans should not eat GM food" we should take it to mean
no health reason, since those kinds of reasons are the only ones under consideration
at this point.

Once we accept these implied facts, the non sequitur disappears. It does follow
from the fact that lots of research – enough for us to trust the results – says
that GM food is safe, that there is no good health reason not to eat it.

What the Economist leader demonstrates is how it can sometimes be too
easy to identify bad argumentative moves in forms of writing that are not written
for a readership of pedantic logicians. Has this series been guilty of identifying
non sequiturs only by ignoring the premises and assumptions which are obviously
implied if only one cares to look? I’ll let you be the judge of that.