But even if it were desirable to make -general observations- not
necessary to decide the questions presented, I cannot subscribe to
some of the observations made by the Court.  In Part II-B, the
Court concludes that reliability and relevancy are the touchstones
of the admissibility of expert testimony.  Ante, at 9.  Federal
Rule of Evidence 402 provides, as the Court points out, that
-[e]vidence which is not relevant is not admissible.-  But there is
no similar reference in the Rule to -reliability.-  The Court
constructs its argument by parsing the language -[i]f scientific,
technical, or other specialized knowledge will assist the trier of
fact to understand the evidence or to determine a fact in issue .
. . an expert . . . may testify thereto . . . .-  Fed. Rule Evid.
702.  It stresses that the subject of the expert's testimony must
be -scientific . . . knowledge,- and points out that -scientific-
-implies a grounding in the methods and procedures of science,-
and that the word -knowledge- -connotes more than subjective belief
or unsupported speculation.-  Ante, at 9. From this it concludes
that -scientific knowledge- must be -derived by the scientific
method.-  Ante, at 10.  Proposed testimony, we are told, must be
supported by -appropriate validation.-  Ante, at 10.  Indeed, in
footnote 9, the Court decides that -[i]n a case involving
scientific evidence, evidentiary reliability will be based upon
scientific validity.-  Ante, at 10, n. 9 (emphasis in original).
  Questions arise simply from reading this part of the Court's
opinion, and countless more questions will surely arise when
hundreds of district judges try to apply its teaching to particular
offers of expert testimony.  Does all of this dicta apply to an
expert seeking to testify on the basis of -technical or other
specialized knowledge--the other types of expert knowledge to which
Rule 702 applies-or are the -general observations- limited only to
-scientific knowledge-?  What is the difference between scientific
knowledge and technical knowledge; does Rule 702 actually
contemplate that the phrase -scientific, technical, or other
specialized knowledge- be broken down into numerous subspecies of
expertise, or did its authors simply pick general descriptive
language covering the sort of expert testimony which courts have
customarily received?  The Court speaks of its confidence that
federal judges can make a -preliminary assessment of whether
the reasoning or methodology underlying the testimony is
scientifically valid and of whether that reasoning or methodology
properly can be applied to the facts in issue.- Ante, at 12.  The
Court then states that a -key question- to be answered in deciding
whether something is -scientific knowledge- -will be whether it can
be (and has been) tested.-  Ante, at 12.  Following this sentence
are three quotations from treatises, which speak not only of
empirical testing, but one of which states that -the criterion of
the scientific status of a theory is its falsifiability,
or refutability, or testability,- ante, pp. 12-13.
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