The following from a 1932 book on canon law, might shed light on the status of Pope Liberius after he capitulated under duress and signed a semi-Arian creed:
Somewhat more complicated is the case
of a Catholic who denies his faith exteriorily in face of public or private
persecution, but interiorily retains completely his faith in what he denies.
His words or acts are really lies of a particular scandalous nature, and a
violation of the commandment of external profession of faith. There is no
question as to the seriousness of the sin he commits; but it is likewise clear
that it is not a sin of heresy, since interiorily he retains and actually
renews his faith in the dogmatic truth he exteriorily denies. Moralists
therefore teach that he has not committed a sin of heresy, and therefore is not
bound, in the internal forum, by the censures which the Church attaches to
heresy. Canonists admit this teaching in theory, but are careful to add that in
the external forum he has professed heresy (or apostasy), and has therefore
made himself liable to the punishments inflicted on those guilty of these
delicts. In actual practice, the main distinction between formal heretics and
those who deny their faith under pressure, would seem to be that the latter
will be more anxious to regain communion with the Church, and more ready to
withdraw contumacy, and hence to seek and obtain absolution in both the
internal and external fora. (Eric F. MacKenzie, The Delict of Heresy In Its
Commission, Penalization, Absolution [Canon Law Studies 77; Washington,
D.C.: The Catholic University of America, 1932], 36)
