> 1.  Does anyone know the origin of the knock on wood for luck superstition?
 
According to _Heavens To Betsy & Other Curious Sayings_, by Charles Earle
Funk (NY: Harper & Row, 1983):
 
TO KNOCK ON WOOD
        Why do even those among us who loudly proclaim utter freedom from
superstition feel just a bit reluctant to state that such-and-such
calamity has never happened without immediately feeling an urge to tap on
some solid piece of wood?  As everyone knows, the act is supposed to
avert evil or misfortune which otherwise might attend vainglorious speech.
        No one knows how the superstition arose, but Geoge Stimpson, in
_A Book About a Thousand Things_ (1946), which the publishers, Harper &
Brothers, jpermit me to quote, presents some of the numerous theories
that have been offered.  He says:
        ...Some attribute it to the old game known as "touching wood" or
"wood tag," in which a player who succeeds in touching wood is safe from
capture.  Others hold that this game and "knocking on wood" had a common
origin in primitive tree worship, when trees were believed to harbor
protective spirits.  To rap on a tree--the dwelling place of a friendly
spirit--was to call up the spirit of the tree to protect one against
impending misfortune.  Later, people would place the hand on a wooden
statue of a diety for the same purpose.  It is said that among certain
European peasants it is still common to knock loudly on wood to keep away
evil spirits. Still others believe the superstition is of Christian
origin and that it is in some way associated with the wooden cross upon
which Jesus was crucified.  Perhaps, they think, it is a survival of the
religious rite of touching a crucifix when taking an oath or the beads of
the rosary when praying.
 
I also found this entry in _Brewer's Dictionary of Phrase and Fable_, by
Ivor H. Evans.  Revised edition. (London: Cassell, 1981.
 
TO TOUCH WOOD.  An old superstition to avert bad luck or misfortune or to
make sure of something good; also when feeling pleased with one's
achievement or when bragging.  Traditionally, certain trees such as the
oak, ash, hazel, hawthorn and willow had a sacred segnificance, and thus
protective powers.  Properly these should be the ones touched but this
detail has largely passed into oblivion and any wood is put to use.
Often, jocularly, the forehead is touched.
 
 >
> and now the difficult part ...
>
> 2.  Does it matter if the wood is alive or dead?  (i.e., a board as
> opposed to the actual tree) and does the size of the wood have any
> bearing on the matter?
 
Whether or not this matters depends on which of these origin theories you
believe.  Maybe touching you forehead is just as good! ;)
 
Carol