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␈↓ ↓H␈↓␈↓βS␈↓∧ Artificial Intelligence Laboratory, STANFORD UNIVERSITY, Stanford, California 94305

␈↓ ↓H␈↓∧Telephone 415 497-4430␈↓ 
&June 4, 1977 




␈↓ ↓H␈↓Professor Nicholas Rescher
␈↓ ↓H␈↓Department of Philosophy
␈↓ ↓H␈↓University of Pittsburgh
␈↓ ↓H␈↓Pittsburgh, PA

␈↓ ↓H␈↓Dear Professor Rescher:

␈↓ ↓H␈↓        You␈α
may␈αbe␈α
interested␈α
in␈αthe␈α
enclosed␈α
paper.␈α What␈α
makes␈α
me␈αthink␈α
so␈α
is␈αyour␈α
paper␈αin␈α
the
␈↓ ↓H␈↓volume␈α⊂of␈α⊂essays␈α⊂honoring␈α∂Hempel.␈α⊂ In␈α⊂that␈α⊂paper␈α⊂you␈α∂argue␈α⊂that␈α⊂certain␈α⊂concepts␈α⊂cannot␈α∂be
␈↓ ↓H␈↓de≡ned␈αwithout␈αassuming␈α
minds.␈α I␈αthink␈α
the␈αconsiderations␈αyou␈α
advance␈αare␈αimportant␈αbut␈α
admit
␈↓ ↓H␈↓a␈α
di≥erent␈αinterpretation␈α
-␈α
namely␈αthat␈α
certain␈α
concepts␈αare␈α
not␈α
de≡nable␈αin␈α
themselves␈α
but␈αonly␈α
as
␈↓ ↓H␈↓part␈α∞of␈α∞a␈α∂theory.␈α∞ A␈α∞theory␈α∂is␈α∞a␈α∞complex␈α∂mathematical␈α∞structure,␈α∞and␈α∂one␈α∞might␈α∞be␈α∂inclined␈α∞to
␈↓ ↓H␈↓argue␈αthat␈αsuch␈αtheories␈αpresuppose␈αminds,␈αbut␈αthe␈αargument␈αwould␈αhave␈αno␈αmore␈αforce␈αthan␈αan
␈↓ ↓H␈↓argument␈αthat␈α
any␈αmathematical␈α
concepts␈αpresuppose␈α
minds.␈α It␈α
further␈αturns␈α
out␈αthat␈αthe␈α
theories
␈↓ ↓H␈↓are␈α
often␈αonly␈α
approximate,␈α
and␈αa␈α
concept␈αde≡ned␈α
in␈α
terms␈αof␈α
a␈αtheory␈α
may␈α
not␈αbe␈α
de≡ned␈α
in␈αa
␈↓ ↓H␈↓better␈αapproximation␈αto␈α
reality.␈α I␈αargue␈αthat␈α
many␈αcounterfactual␈αstatements␈αhave␈α
that␈αcharacter
␈↓ ↓H␈↓which makes them seem to vanish when examined too closely.

␈↓ ↓H␈↓        Please␈αexcuse␈αany␈αevidence␈αof␈αinexperience␈α
with␈αphilosophy.␈α I␈α≡nd␈αmyself␈αdriven␈α
to␈αthink
␈↓ ↓H␈↓about␈αthese␈αquestions␈α
by␈αthe␈αrequirements␈α
of␈αresearch␈αin␈α
arti≡cial␈αintelligence.␈α Any␈αcomments␈α
will
␈↓ ↓H␈↓be appreciated.


␈↓ ↓H␈↓Sincerely,



␈↓ ↓H␈↓John McCarthy
␈↓ ↓H␈↓Director
␈↓ ↓H␈↓Professor of Computer Science