Qfyilyi

You commonly hear "under false pretences" ("pretenses" in AmE). I was originally thinking of what police did when making a phone call to someone they wish to incriminate, which is called a "pretext call", and I noticed "pretext" isn't preceded with "false". To find the meaning "pretence/pretense" I looked up their definitions:

pretense
noun

1.
a.A false appearance or action intended to deceive: "He ran the back of his hand up her cheek, with the pretense of wiping away
sweat"
b.A professed but feigned reason or excuse; a pretext: left
the room under the pretense of having to make a phone call.
American Heritage Dictionary

pretence
noun

1.a false show of something; semblance: a pretense of friendship.

2.a pretending or feigning; make-believe: My sleepiness was all pretense.
Collins Dictionary

This is my opinion, but many redundant or tautologous terms are frowned upon from a stylistic point of view, however it doesn't seem to me that "false pretence(s)" is eschewed with as much disdain as many other seemingly redundant terms.

A Google NGram search shows that "under the false pretence/pretense" is much less frequent than simply "under the pretence/pretense", while "under false pretences/pretences" is extremely more frequent than simply "under pretences/pretenses".

I feel that some "supposed" redundant terms are warranted if they add any extra information at all, or if an adjective or adverb intensifies the noun or verb it's modifying. Some of the examples here (200 Common Redundancies in English) of redundant terms I feel are justified. For example:

eradicate (completely) - I see "completely" as an intensifier rather
than adding information, it's emphasis, maybe as to intent, resolve or something else.

best (ever) - Both acts as intensifier, and possibly adds extra information,
such as best this season or in the history of basketball.

(final) outcome - Possibly adds extra information. If you consider a
process a multi-stage affair and both each stage has an outcome and
also the totality of the stages has an outcome. The final could specify that it's referring to end of the whole multi-stage process as distinct from one of the stages.

In other cases I tend to view the "supposed" redundancy as unnecessary, such as:

consensus (of opinion)

Is "false pretence" a redundancy, as I actually tend to believe it is? Also what is it about this particular phrase that has made it so popular and acceptable to many people? Is it just a case of it being a set phrase or popular collocation that it has gained currency, and so no matter how redundant it's just stylistically acceptable?

Also, as for "pretext", Google NGrams shows that "under pretext" is much more frequent than "under false pretext", however if we compare the plural "pretexts", ie., "under false pretexts" and "under pretexts" we find the results to show roughly the same frequency.