Some thing or fact P
has relevance for some fact or thing Q, or is relevant for it, if the truth of
P makes a difference to the truth or
probability of Q.
The concept of relevance is very important, and often neglected. The
reason that it is important is that anything whatsoever may be relevant to
anything whatsoever, and we need to somehow settle what is and is not relevant
for the theories and
guesses we entertain or consider.
As stated, the definition conforms to the one that is used in standard
probability theory - which
that (i) P is relevant to itself (ii) P is relevant to ~P and (iii) P is
relevant to Q if the probability of Q if P is not the same as the probability
of Q if ~P.
There are more subtle definitions of
irrelevance and independence in
And in a wider sense, perhaps, also including
desires, values or
feelings, relevance is very important
too for human reasoning, as is also
wishful thinking, that tends to be
caused by confusions of what is
what is personally and
A final remark that should be made is that
the term "relevance" is much abused in political and bureaucratic
rhetorics: One very common rhetorical move to avoid unpleasant questions or
conclusions is to declare them "irrelevant" (as if the speaker has the
divine right of deciding this); another common rhetorical move to plug plans
and proposals that are useful only or mostly for those who propose them is to
insist loudly on their "(social) relevance". One normally can see
through this - just as with advertising phrasess like "X is more valuable" -
by asking for what or for whom or by what standard?