This article is from the alt.usage.english FAQ, by Mark Israel firstname.lastname@example.org with numerous contributions by others.
Many phrases often criticized as "redundant" are redundant in
most contexts, but not in all. "Small in size" is redundant in most
contexts, but not in "Although small in size, the ship was large in
glory." "Consensus of opinion" is redundant in most contexts, but
not in "Some of the committee members were coerced into voting in
favour of the motion, so although the motion represents a consensus
of votes, it does not represent a consensus of opinion."
Context can negate part of the definition of a word. "Artificial
light" is light that is artificial (= "man-made"), but "artificial
flowers" are not flowers (i.e., genuine spermatophyte reproductive
orders) that are artificial. In the latter phrase, "artificial"
negates part of the definition of "flower". The bats known as
"false vampires" do not feed on blood: "false" negates part of the
definition of "vampire".
The ordinary definition of "fact" includes the idea of "true"
(e.g., fact vs fiction); the meaning of "fact" does have other
aspects (e.g., fact vs opinion). Context can negate the idea of
"true". Fowler himself used the phrase "Fowler's facts are wrong;
therefore his advice is probably wrong, too" (a conclusion that he
was eager to avert, moving him to defend his facts) in one of the
It follows that "true fact" need not be a redundancy.