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What is the ¬ symbol on a British Windows keyboard called? You get to it by pressing Shift and the key left of the '1'.

keyboard layout

David
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David
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1 Answers1

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As far as I'm aware, I've always seen this referred to as a negation symbol. That is its primary use: to negate a logical evaluation in formal logic.

SoftwareEngineering.SE seems to agree with me:

The only use I've seen for the ¬ symbol is to represent negation in the context of formal logic. For instance, if P is the proposition "It will rain today", then ¬P is the proposition "It will not rain today." I've also seen ~ used for this.

Also note the first comment in the linked post:

That character is U+00AC NOT SIGN and is one of the many notations for logical negation.

Unicode does indeed list this character as "NOT SIGN", which is shorthand for "negation symbol".

Flater
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  • So, was this symbol on typewriter keyboards in Britain before the days of home computers? Before the days when a common person would know anything about symbolic logic? – GEdgar Sep 15 '17 at 12:25
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    I've also seen it called "EBCDIC NOT", because it was generally used on IBM mainframe computers (which used the EBCDIC character set), but not on minis and micros (which generally used ~ and the ASCII character set). – Jeff Zeitlin Sep 15 '17 at 12:30
  • @GEdgar: Note that George Boole published The Mathematical Analysis of Logic in 1847, well ahead of the advent of home computers. However, I can't see the symbol on any picture I've looked at, so far. The fact that symbols like ½ are actually found on the typewriter makes me suspect that a typewriter's keys may have been tailored to fit a financial context, but not necessarily a mathematical or computational one. – Flater Sep 15 '17 at 12:35
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    @JeffZeitlin I believe this is why it's found on computer keyboards today. It was necessary on IBM mainframes running PL/I, and when IBM started making consumer keyboards they brought the same key set. – TroyHurts Sep 15 '17 at 13:49
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    MS Word has this sign as "optional hyphen" but i don't know if this was the original meaning of this character, othe than the use in logic – Stefan Sep 15 '17 at 18:45
  • @TroyHurts: seems unlikely to be the reason. Wouldn't it be on US keyboards too? And is it on XT keyboards? – rjpond Sep 15 '17 at 18:47
  • Huh, in practice I’ve only ever seen this to be the ‘show hidden characters’-mode way of representing a manual line break. Never knew it was a negator… – Janus Bahs Jacquet Sep 15 '17 at 18:59
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    @rjpond That's a good point about US keyboards. If I had to hazard a guess, perhaps the introduction of BS 4822 in 1980, against which UK keyboards are standardised, came at a time when IBM layouts with ¬ were more commonplace in the UK than the US, but trends continued to change in the US before the design we have today solidified. This is total conjecture, however. – TroyHurts Sep 18 '17 at 08:28