Document ID: ./input/supremecourt_opinions/opinions/boundvolumes/529bv.pdf
Page Number: 626

529US2

Unit: $U52

[09-26-01 10:36:40] PAGES PGT: OPIN

Cite as: 529 U. S. 513 (2000)

551

Opinion of the Court

competent to testify unless corroborated by another wit-
ness). Plainly, the imagined rule does not mean that Fen-
wick’s case is not an example of an ex post facto law. But if
that is so, why should it be any different for Article 38.07?
Just as we can imagine a witness competency rule that would
operate similarly to the statute in Fenwick’s case, the above
argument imagines a witness competency rule that operates
similarly to Article 38.07.
If the former does not change our
view of the law in Fenwick’s case, why should the latter
change our view in the present circumstances?

Moreover, the argument fails to account for what Calder’s
fourth category actually says, and tells only half the story of
what a witness competency rule does. As for what Calder
says, the fourth category applies to “[e]very law that alters
the legal rules of evidence, and receives less, or different,
testimony, than the law required at the time of the commis-
sion of the offence, in order to convict the offender.” 3 Dall.,
at 390 (emphasis deleted). The last six words are crucial.
The relevant question is whether the law affects the quan-
tum of evidence required to convict; a witness competency
rule that (in certain instances at least) has the practical
effect of telling us what evidence would result in acquittal
does not really speak to Calder’s fourth category.

As for relating only half the story, the dissent’s argument
rests on the assertion that sometimes a witness competency
rule will result in acquittals in the same instances in which
Article 38.07 would also demand an acquittal. That may be
conceded, but it is only half the story—and, as just noted,
not the most relevant half. The other half concerns what a
witness competency rule has to say about the evidence
“required . . . in order to convict the offender.” The answer
is, nothing at all. As mentioned earlier, see supra, at 546–
547, prosecutors may satisfy all the requirements of any
number of witness competency rules, but this says absolutely
nothing about whether they have introduced a quantum of