This is a backslash \.

If you read the slash from left to right it starts at the top and goes down - hence it is a downslash.

If you read the slash from top to bottom it starts on the left - which in our culture represents back direction - and continues to the right - which represents the forward direction. Hence it is a forward slash.

So why do we call in a backslash?

The reason for my question is that whenever I am not sure if I am looking at a forward slash or a backslash I am trying to reason about its direction which apparently fails. I believe that this classifies it as an usability problem.

PS: I am deriving the meanings of the directions from things like direction of writing, clock dial, rulers, time scales, calendars, play buttons etc. Left is past, back, right is future, forward.

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    @Lan I imagine if you called it a Solidus in conversation you would get a lot of blank looks... – Midas Apr 6 '16 at 17:27
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    I have literally never heard it called "solidus" before. Or maybe I have and I just forgot (and will once again forget about 20 seconds after I press the "add comment" button). – fluffy Apr 6 '16 at 17:32
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    Pretend the slash is a pencil you're holding with the tip touching the ground. When you let go, the \ pencil falls backwards and the / pencil falls forwards. – user1717828 Apr 6 '16 at 18:06
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    Note that for right-handed people in a left-to-right language, slashes are much easier to write than backslashes, so it makes sense to think of the back one was the weird one. – Mehrdad Apr 6 '16 at 19:05
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    I'm voting to close this question as off-topic because it doesn't appear to have anything to do with UX. It asks about the history of the name for a term rather than asking about UX-related things like (1) the history/origins of its use or (2) the current terminology for an interface element with an unknown name. It might be on topic at English.SE. – Graham Herrli Apr 6 '16 at 20:31

11 Answers 11

up vote 14 down vote accepted

Ancient slash → new back-slash → disambiguating retronym forward slash

Ancient Roman coins - Solidus and Denarius.

The slash character came first, with a different formal name solidus. This name comes from Latin and was associated with coinage - hence (I guess) it's use in writing down prices in older currencies: 10/6 was quite a common notation for prices in British currency pre-decimalisation. The solidus mark probably indicates the first number is units of solidus, the second of denarius. Or in the British case: shillings and pence. Note common first letter abbreviations s and d were used in Britain (also £ is L for Latin libra).

The slash (or solidus) was around for a very very long time before the reversed version was invented. The reversed version therefore acquired the more informal name back-slash to indicate a reversed form of slash.

The name "forward slash" has probably evolved since the general public started to use computer keyboards incorporating two characters that look like a slash. There was a need to disambiguate slash for people who didn't learn about computers in a formal teaching context.

The Medieval comma, Johannes Gutenberg and Aldus Manutius

The history of the slash and the comma are intimately intertwined. Both have been used to separate items of text or to separate numbers with different units. In some European countries it is normal to use the comma where others use a decimal point - to separate whole units from decimal fractions. So you might see €5,60 as a price. The comma serving much the same role as the slash (or solidus) in 10/6.

It is easy to find history linking the two. For example

The [comma] mark used today is descended from a diagonal slash, or virgula suspensiva ( / ), used from the 13th to 17th centuries to represent a pause. The modern comma was first used by Aldus Manutius

I have also seen the reverse stated, that the slash is derived from the comma.

I believe that the earliest movable-type printing presses, as used by Johannes Gutenberg used commas in some situations where we would today normally use slashes. So his fonts did not have slashes, only commas.

Gutenberg's font

1899 - Adler typewriter company.

enter image description here
- Photo © Dake - CC-by-SA 2.5

Slash, but no backslash.

C20th - Monotype corporation

enter image description here Monotype Matrix Case, Arrangement No 841

No slashes or backslashes in moveable type typography? But note the comma.

1963 - Telex

enter image description here
ASR-32 teleprinter for Telex, CC BY 2.0, Arnold Reinhold

Slash but no backslash.

1963 - American Standard Code for Information Interchange (ASCII)

American Standards Association (ASA) X3.4 subcommittee

/   slant
\   reverse slant

1991 - Unicode consortium

002F   /     SOLIDUS
             = slash, virgule

             = backslash.

So it is clear that the name backslash was introduced to indicate a novel character that was the reversed version of a long established character.

The name forward slash therefore subsequently became needed to disambiguate the name for the earlier character.

  • +1 for the linguist's answer. particularly for using the word retronym (albeit not in a sentence). – james turner Apr 14 '16 at 0:04

You have a stick, |, in your mind (AKA a pipe character).

\ lean it back - will fall back = back slash

/ lean it forward - will fall front = forward slash

Font features can be grouped as thickness, slant and width as in Google fonts. The natural way of writing is to lean forward which is named as slant.

Slant is one of the synonyms of slash[2,3]. Here is forward-slanted natural handwriting:

Forward slanted handwriting

[2]: "slant, n.¹", Oxford English Dictionary, 1st ed., Oxford: Oxford University Press, 1911.
[3]: A slash by another name:

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    Indeed. It is called a back slash, because it is sloped back against the direction of writing, in contrast to the common slash. Source: – Bart Gijssens Apr 6 '16 at 14:14
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    This is a useful way to remember which is which, but it does not answer the question of why the characters are named the way they are. – Bobwise Apr 6 '16 at 15:43
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    @KRyan The answer speaks to this statement from the OP: whenever I am not sure if I am looking at a forward slash or a backslash I am trying to reason about its direction – plainclothes Apr 6 '16 at 20:48
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    It's only a natural slant if you're right handed. For us lefties, it's a pita scrunching so as not to smudge ink. Of course, modern biros are a lot better, but I miss cartridges. – Phil Lello Apr 6 '16 at 22:29
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    Let it be known that it was in 2016 that the internet had to be reminded that once, long ago, the characters we see now on our computer screens were once drawn, literally, by hand. Those primitive beings named the backslash so because in order to draw one you had to raise your flesh from the paper with the force of 1000 keyups, move your arm BACKwards, and then strike down with the force of a form.submit() – J.J Apr 9 '16 at 21:45

Because slashes (/) were around long before their backwards counterpart came along.


Well, it was a nice theory, but according to Wikipedia:

  • "The name "slash" is a recent development, first attested in American English c. 1961 ref
  • "Bob Bemer introduced the "\" character into ASCII on September 18, 1961, as the result of character frequency studies." ref Bemer's own account

The / symbol was around for centuries before it got this name, which (I'm guessing) contributed to it getting the unmarked "slash" name while the novel \ got the marked "backslash" name.

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    sorward slash? Like, a flying slash? cool... – theonlygusti Apr 6 '16 at 15:17
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    @BartGijssens / is a slash. `` is like a slash but a mirror image, i.e. backwards. So it's a backwards slash or 'backslash'. If I said, I have this new letter that looks like a K but it's backwards, you wouldn't say, "Great let's name it the 'forwards K'". – Theodore Norvell Apr 6 '16 at 17:49
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    < and > were presumably invented at the same time. It's more like how we'd call ? "question mark" and ¿ "upside-down question mark" because the latter are much more recent (for English speakers at least). – Steve Bennett Apr 7 '16 at 1:01
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    This really is the correct answer. Slash, with this name, existed on keyboards and in typography for a very long time before the backslash character became common. It was introduced to permit printing/typing fractions on a single line -- 2/3, for example -- just as the @ character became common because it was already in use as a commercial shorthand for "each" abbreviated ea. ("At" is a back-formation from pricing shown as "5 @ $1.00, $5.00 total". ). So slash was preexisting.When " \" was added, there were several colloquial names for it; backslash is the one which survived. – keshlam Apr 7 '16 at 1:16
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    Even if the name "slash" came into use a the the same time "\" entered ASCII in 1961, most people weren't using computers then and my memory is that "/" was a standard symbol on typewriters while "\" was a specialized computer symbol. I'm also not sure this is a usability issue as much as an issue of language which isn't designed according to usability principles. – Marc Stober Apr 8 '16 at 14:29

This character has many different names, and back slash is just the oposite of slash, nothing else. It was initially created to represent signs in ALGOL language that functioned as AND and OR operators

Bob Bemer introduced the "\" character into ASCIIon September 18, 1961,as the result of character frequency studies. In particular the \ was introduced so that the ALGOL boolean operators ∧ (AND) and ∨ (OR) could be composed in ASCII as "/\" and "\/" respectively. Both these operators were included in early versions of the C programming language supplied with Unix V6, Unix V7 and more currently BSD 2.11.

so, it has nothing to do with leaning back or forward, but it was originally conceived as just the remaining part of the logical disjunction/ conjunction math signs, and while its real name is reverse solidus, it has many different names besides back slash

It is sometimes called a hack, whack, escape (from C/UNIX), reverse slash, slosh, backslant, downhill, backwhack, and in rare occasions, bash, reverse slant, and reversed virgule

Source: Back Slash

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    it has nothing to do with leaning back or forward < Of course it does. Just like it's alternate name "backslant" implies, it leans backward. – plainclothes Apr 6 '16 at 15:37
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    A backslash is not a reverse solidus. A backslash is "straighter" than a reverse solidus. – Lan Apr 6 '16 at 16:28
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    This answer really just covers the origin of the symbol itself, not the origin of the term 'Backslash'. – JonW Apr 6 '16 at 16:36
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    @Lan The official, formal Unicode for the \ is REVERSE SOLIDUS, and Unicode does not have a character with the name BACKSLASH. – Mr Lister Apr 7 '16 at 14:05
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    @MrLister I didn't know unicode conflated them. Thanks. Wikipedia says "The solidus is similar to another punctuation mark, the slash, which is found on standard keyboards; the slash is closer to being vertical than the solidus. These are two distinct symbols that have entirely different uses. " – Lan Apr 7 '16 at 14:21

The reason you're confused is because you're using the wrong definition of "back". Or rather, the wrong reference frame to apply the word "back" to.

You are apparently using the direction of writing, that is to say from left to right, to apply the word "back" to. But in terms of direction, the word "back" has two meaning:

  1. The opposite of "forward".

  2. Opposite or reverse.

The word "back", apart from meaning the opposite of forward, actually itself can simply mean "the opposite direction".

There is no "Forward Slash"

Technically, "forward slash" did not exist. It only came about retroactively after the term "backslash" was coined. The original name for "forward slash" was simply "slash". It is with reference to slash that the word "back" was applied. It simply means "reverse slash".

Back to your problem

So, if backslash means reverse-slash, how to know which direction "slash" slants to?

I don't really know much about your culture but for me slashes are what we use to write dates and street addresses:

date: 1/1/2016
place: No. 10, 14/24 street, Section 14, Petaling Jaya.

So that's what I use to remember "slash" - it's what people normally use: "/". So "backslash" is what people don't normally use" "\".

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    Reverse-Slash is The Slash's greatest enemy. – John Clifford Apr 7 '16 at 8:42
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    @JohnClifford yeah, if you put them together, they annihilate: X – user67695 Apr 7 '16 at 13:43
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    Is it worth mentioning that slash is also commonly used in fractions: 1/4, 1/3, 1/2, 2/3, 3/4, etc.? – Robert Fisher Apr 7 '16 at 18:08
  • @RobertFisher: Yeah, I wasn't sure if that style of writing fractions is recent development (influenced by the divide operator in programming languages?). Traditionally I'd write a fraction with a horizontal line rather than a slash. – slebetman Apr 7 '16 at 23:12
  • @slebetman Fair point. The wikipedia article suggests that it was adopted from using a solidus between shillings and pence. Although I (a child of the 1970s) saw these style of fractions long before I was introduced to ones with a horizontal line in math class (c. ?) or the division operator in programming (c. 1979). So, I assumed it was old enough to be familiar to most. – Robert Fisher Apr 8 '16 at 15:58

The verb to slash comes from the Middle French esclachier and means to cut with a single sweeping motion. If you hold a knife or sword and slash something in front of you like a curtain or an enemy, and you are right handed like most people, the wound will be from top right to bottom left. Think of the middle part of the Z in Zorro.

Back means the other way.

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    Yeah, but the wound will start at the person's left shoulder... See? We have been looking at this from our point of view all along, when we should have been taking the character's point of view. No wonder writing is so hard to understand! We have been reading it backwards! Er, I mean, the wrong way round. – user67695 Apr 10 '16 at 21:57

My mnemonic for recalling this is to visualize the slash as a person viewed from the side. The person would face forward in the direction of reading with the head at the top and feet at the bottom of the written line. A pipe | stands straight while a backslash \ leans back.

Alternatively I (dimly) recall that a slash follows handwritten forward slanting, and a backslash crosses that, as has been mentioned.

  • This is how I used to teach it. History completely aside this helped English speaking students remember it so they could follow spoken instructions. – candied_orange Apr 8 '16 at 3:42
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    That's a very dextrous explanation :-). When you say "from the side" you assume without noticing that this means "from their right side". A more sinister or gauche observer may visualise viewing said person from their left side :-). – Russell McMahon Apr 8 '16 at 15:43
  • @RussellMcMahon thats dumb because the "person" wouldnt be walking against the flow of the text – Steven Penny Apr 9 '16 at 13:27
  • @StevenPenny Without desiring to be confrontational - Labelling something as "dumb" often can mean that one does not see things in the way described and cannot imagine that anyone else would either. In such cases, "smart" MIGHT be seeing that some people may see & think quite differently, even though it does not seem to make sense. (People tend to be like that :-) ). | What seems to be an excellent example of this is given in the OP's original question. His description of why he sees a \ as a forward-slash is utterly foreign to my way of thinking - but this whole discussion arises from that. – Russell McMahon Apr 9 '16 at 16:18
  • @RussellMcMahon yeah, you are on to something. We should be viewing the text from what we would call "behind it" and looking outward toward the reader's eyes. In that way, the text direction would still be "forward", except that it would go to the left now... So, it appears that some people are actually "inside" their computers, which leads to the different views on this question. Of course, it is bigoted to call something "inside" or "outside", as it presumes a preferred viewpoint. Best not to say anything at all. – user67695 Apr 10 '16 at 22:02

If you are right handed, \ is annoying to write, while / is easier, which is why / became the separator symbol of choice in the days before computers and typewriters. It came to be called slash. In a UX sense, the canonical name is given to the more common variant, which is more common because it is more ergonomic.

\ looks like the a slash that's backwards, so presumably this is why it came to be called a backslash.

Why is backslash called BACK slash when arguably it points forward?

I would be very frightened of encountering these supposed persons who engage in arguments over which way the backslash points.

But in any case, the point is not which way it points. The symbols are opposites of each other, so you pick a dominant one and define the other in relation to the dominant. Clearly / makes more sense to choose as the dominant symbol: It is easier to write, it is more common, it has more meanings and is appropriate in more contexts than \, not to mention that it is older.

The answer to this question is hidden in the mists of time, but I, your intrepid explorer, have braved the journey[1] and returned to supply you with the One True Etymology for "backslash".

[1] I have not literally traveled back in time.

It all starts with the shilling. You remember the shilling, if you were born before circa 1970. The British unit of currency used to be the pound sterling, which was divided into twenty shillings. Each shilling was further divided into twelve pence. There were also one-hundred-twenty ha'pence to a crown, one-thousand-eight farthings to a guinea,… but I digress. (In case you were wondering what J.K. Rowling was spoofing with her seventeen sickles to a galleon and twenty-nine knuts to a sickle, now you know.)

The common way of referring to a quantity of currency less than a pound was with the word "and". For example, two shillings and threepence would be called "two and three". This was written with a / mark, for example 2/3.

Now, the & got angry. It had long been used for "and", and it maintained that if people say "two and three" then they should write 2&3. It went over to the 2/3 and tried to pull the / out. But the figures (digits) liked the /: it was nice and slender, and they were afraid that they would be too crowded with an &. So they hung on to the /, not allowing the & to pull it out.

So the & came up with another plan. It went to the Queen and tried to plead its case. It wanted the government to introduce a public bill to Parliament mandating that shillings-and-pence amounts be written using & only and never /. The Queen thought it was a grand idea and set her Chancellor of the Exchequer, Peter Thorneycroft, on it.

Well, the bill failed to pass. But while it was in process in Parliament, Thorneycroft got really into the idea, and set about enforcing it before it even became law. (This is why he wound up resigning his position.) He sent his employees around to all the shops with instructions to whip the chest of anyone who was seen writing 2/3. The chest was chosen because it was most convenient: the government employee was in front of the person, so he could see him writing, so he whipped his front.

At that time, the / became known as a "front's lash". So naturally the \ was called a "back's lash".

It's simple, the 'slash' / came first. Then keyboards & computers came up with one that pointed the other direction. So, what to call it? BACKSLASH \

Computers used it and 'invented' it because they wanted a character that was NOT currently being used in normal language.

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    -1 because this not only repeats what other "answers" have already said, but it also fails to provide any historical evidence. – Graham Herrli Apr 8 '16 at 20:54

I think in this case of a Forward Slash or Backslash, it is seen basically from the POV of:

/ = Forward Slash -> top pointing right, so "forward"

\ = Backslash -> top pointing left, so "backward"

I think it has to do with the western left-to- right reading custom as well as the human experience of gravity:

If the Slash was a stick, a Forward Slash would fall towards the right, while a Backslash would fall towards the left

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    -1 because this not only repeats what other "answers" have already said, but it also fails to provide any historical evidence. – Graham Herrli Apr 8 '16 at 20:46
  • historical evidence? Only one answer even attempts to that direction, and even he doesn't provide "evidence"... Whatever... – localhost Apr 8 '16 at 23:25

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