When we reason about the truth or falsity of a conclusion, we
rarely consider the conclusion in a vacuum. Instead, we have in
mind a range of other possible conclusions. When we think about
whether to take a certain action, we weigh it against other
actions. When we consider a hypothesis to explain why something
happened, we test it against other hypotheses. In short, thinking
often involves a choice among alternatives.
The fallacy of false alternative occurs when we fail to consider
all the relevant possibilities.
One form occurs when we consider only the extreme points of a
scale. If you told me that Diane is not rich, I would commit the
fallacy if I inferred that she is poor. Rich and poor are the
extremes on a scale that contains many intermediate degrees of
The most subtle examples of the fallacy are those in which
relevant alternatives are excluded by some implicit, unspoken,
and thus invisible assumption.