Just as an example, let's say we have 60 BPM. So every second there's a beat. Imagine nodding your head every second to this rhythm.

Now isn't that enough information to make a song? If I have a metronome at 60BPM then I can rap over it, or play a melody/harmony over it, without thinking about bars at all.

So why do we take an extra step to group 4 of these beats to make a bar, and then think in terms of bars. Also, say if I change it from (1 bar = 4 beats) to (1 bar = 3 beats), how does that change the song? Because the BPM didn't change.. in the above example, I was just rapping to the metronome.

Edit: When I asked this question it was mainly me trying to produce beats on a DAW and bars/beats/tempo are all over the place and I didn't understand why it was defaulted to four beats in a bar. But it's interesting to read all the different perspectives so answer any way you want.

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    Bars are strongly related to time signatures, so this might be relevant: music.stackexchange.com/questions/31745/… – topo Reinstate Monica Apr 22 '18 at 21:06
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    Saw this in HNQ and thought you were asking about bars-as-in-alcohol. – David Richerby Apr 23 '18 at 16:06
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    To help understand it from a poet to a rapper, English is a stressed (and, indeed, stress-timed) language. Every word has stressed and unstressed syllables (and, actually, lots more subtlety). I don't mean big, rare stress, just roughly half of syllables are stressed, half not. "I object" and "The object" are different only in their stress, but different words. I'm sure you do this in rap, if you're not a robot! Try listening to your favourite artists (but which is which is not a science). Bars do the equivalent in music, notes in particular positions get accents, like stress in English. – Dannie Apr 23 '18 at 16:39
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    @user6697063 this is part of what rappers call 'flow'. – topo Reinstate Monica Apr 23 '18 at 17:30
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    @user6697063 That content should be posted as an answer, not as a comment. – Todd Wilcox Apr 23 '18 at 18:38

10 Answers 10


First, I think that it would be difficult to read a piece of music with no bar lines. The bar lines help to break longer streams of notes into regularized and easily digestible chunks.

But it is also not true that a stream of 16 quarter notes should represent the same thing as four bars of four quarter notes. For example, typically in 4/4 time the One and the Three get accented, but not the Two and the Four; but of the One and the Three, the One gets a slightly stronger accent. On the other hand, in 2/4 time the One gets accented, but not the Two. All Ones receive the same accent, and all the strong beats receive the same accent. Here the feel is different from 4/4 time. A similar thing happens with 3/4 time compared with 6/8 time. In 3/4 time the One gets the accent, and in 6/8 time the One and the Four get the accents, with the One receiving slightly more emphasis. This means that 3/4 time and 6/8 time have different rhythmic feels.

So bar lines convey some information about rhythmic feel as well as helping to organize notes into easily digestible chunks. Maybe you could preserve time signatures and rhythmic feel without bar lines, but it would be very difficult to read rhythms this way.

Additionally, music tends to have a regular underlying pulse. Musical phrases are played against this pulse. Sometimes the same phrase is placed differently in different passages, or even within the same passage, of the same piece of music. The result is that the same phrase can sound different when played in different locations with respect to the pulse. Players are usually very sensitive to this when performing; jazz players often talk about "playing across bar lines" or will play the same phrase starting on different beats or subdivisions. All of this is really about sound and feel. Bar lines provide a way to represent the regular pulse of the music so that the ways in which phrases fit around it can be more easily seen in written music. In the end, bar lines are really a notational device.

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    I saw this answer in the linked question: music.stackexchange.com/a/31751/48252 and I think the ruler analogy is the easiest to understand, referring to your first paragraph – gl_prout Apr 23 '18 at 9:16
  • Indeed, it is difficult to sight-read music without any bar lines. Depending on the style it doesn't even matter if they're regular, as long as there's some mark between musical phrases. – OrangeDog Apr 23 '18 at 13:14
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    I once wrote a string quartet without a meter signature or bar lines because I wanted the musicians to play it "meanderingly", without any sense of ever arriving at "one". The composition teacher made me put in meter and bars. : ) – Tab Alleman Apr 23 '18 at 20:17
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    Also, imagine trying to rehearse with "let's go from the 47th note of the second page" or "that 22nd F was a bit flat". – OrangeDog Apr 24 '18 at 9:15
  • @OrangeDog -- "it doesn't even matter if they're regular": not sure I can agree with this. One nice thing about bar lines is that they make it easy to see that this collection of quarter notes, eighth notes, sixteenth notes, thirty-second notes, and various rests occupies the same time as that collection of quarter notes. But that only works when bar lengths are regular. I tend think of bar lines as a sort of grid that helps you see how phrases relate to the underlying regular pulse of the music. It is true that even irregular markings would make it easier to find the 47th note of the 2nd page – ex nihilo Apr 26 '18 at 12:28

Please count 1-2-3-4,1-2-3-4, then at the same tempo (speed/ bpm) count 1-2-3-1-2-3.

If you can't feel or tell the difference, then, you're right, there's no need for bars. If you can, then how will someone else know which is which?

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    Ok, so I guess it's mainly for accenting purposes. like it helps us decide which beats to emphasize. – foreyez Apr 22 '18 at 19:19

One bar tends to be the smallest time after which there is some repetition in multiple voices. This is quite a bit of an oversimplification, but it is often observable, in approximate form, in many very different genres.


  • Baroque

    C:Johann Sebastian Bach
    T:Orchestral Suite #3, 3: Gavotte
    %%score T1 T2 A B
    V:T1           clef=treble
    V:T2           clef=treble
    V:A            clef=alto
    V:B            clef=bass
    % 1
    [V:T1] A2 af | g4     A2 ge | f4    A2 ec | d2
    [V:T2] F2 fd | e4     E2 ec | d4    D2 E2 | A,2
    [V:A]  D2 D2 | A4     A2 A2 | A4    A2 C2 | F2
    [V:B]  (D,4   | D,2) C,B,, C,2 A,,2| D,2 D,,E,, F,,2 G,,E,, | F,,2

    Here, the melody voices sequence down the motiv with minim on the 1 and quavers on the 4, the middle voices repeat the simple minim-crotchet-crotchet pattern, and the bass puts quavers on the 2.

  • Classical/Romantic:

    C:Felix Mendelssohn
    T:Symphony #1, 4: Trio
    %%score O T1 T2 B
    V:O            clef=treble
    V:T1           clef=treble
    V:T2           clef=treble
    V:B            clef=bass
    % 1
    [V:O ] [Ec]6            | [FA]6            | [Fd]6            | [Fc]6
    [V:T1] z3       (A c e) | z3       (A d f) | z3       (B d f) | z3                   (A c f)
    [V:T2] (A, C E) z3      | (A, D F) z3      | (B, D F) z3      | (A, C f) z3
    [V:B]  A,, z2    z3      | D, z2     z3      | B,, z2    z3      | F, z2                         z3
  • Blues / Rock'n'Roll accompaniment pattern

    %%score D G B
    V:D            clef=perc
    V:G            clef=treble-8
    V:B            clef=bass-8
    % 1
    [V:D] (3[Ee]ze (3[Be]ze (3[Ee]ze (3[Be]zE |  (3[Ee]ze (3[Be]ze  (3[Ee]ze (3[Be]zE
    [V:G] [A,EAce]2 [A,EAcf]2 [A,EAcg]2 [A,EAcf]2 | [A,EAce]2 [A,EAcf]2 [A,EAcg]2 [A,EAcf]2
    [V:B] A,,2 C,2  E,2 (3F,zE, |  A,,2 C,2  E,2 (3F,zE,
  • Reggae groove

    %%score D G B
    V:D            clef=perc
    V:G            clef=treble-8
    % 1
    [V:D] ze [Be]2 [Ee]e [Be]e | ze [Be]2 [Ee]e [Be]e
    [V:G] z2 [B,FBdf]2 z2 [B,FBdf]2 | z2 [B,FBdf]2 z2 [B,FBdf]2


It's also common to only find repetition after two bars, or already after half a bar. However, one bar is pretty much the shortest delay after which a complete repeat of an accompaniment pattern will sound “proper”.

  • Though correct, that strikes me as a thoroughly inappropriate answer to an (as yet, and no offence intended) musically illiterate rapper! – Laurence Payne Apr 22 '18 at 21:44

To offer a different perspective from the other excellent answers here, I'll draw an analogy between a piece of music and a piece of prose.

Barlines are separators, just like paragraphs and chapters. You can write a perfectly fine essay in one massive paragraph, without losing any semantics conveyed by the individual words within. The existence of paragraphs and chapters however, make it much easier on the reader. It gives an indicator of when a new idea, a new scene or a new argument begins, thereby demarcating the structure of the essay. Similarly, barlines make the pulse of the piece very clear to the musician at a glance. The placement of barlines depends on the music in question; just as you wouldn't cut this sentence

into two with a paragraph break, you wouldn't change the barline placement from (1 bar = 4 beats) to (1 bar = 3 beats), if your music rhythmically repeats once every 4 beats. Barlines assist musicians by providing a guide to the rhythm of the music.

Barlines also aid in referencing. Just as it is convenient to refer to a passage in the book by its chapter number, musicians often refer to music by the bar number. This comes in useful especially in a group rehearsal setting, in order for everyone to begin rehearsing from the same point midway through the piece.

  • I understand that this analogy is not perfect and it breaks down in a lot of ways. But it is still excellent! Sheet without barlines would indeed feel the same as the wall of text without paragraph breaks. – Džuris Apr 23 '18 at 11:57
  • A piece of metrical poetry might be a closer anology – Laurence Payne Apr 24 '18 at 10:15

Well, in a way, you don't need bars. Not for the sort of thing you were describing. If you just set a metronome up and start rapping away, you probably won't have any problems. But if you want to rap with a band, or anyone else, or if you want to write your music down, bars are necessary. There are several reasons for the concept of bars:

  • Communicating metrical information. With your 60 BPM example, changing the meter actually does affect a lot about the song. Think about a waltz vs. a march. In a waltz, which is in 3, you count

1 2 3 |1 2 3...

With an assumed metrical accent on the first beat of each measure. A stead pulse from a metronome does not carry this information.

What if you had it in groups of four? Then, in most western circles, you would get:

1 2 3 4 |1 2 3 4...

In these examples the BPM did not change, however the feel of the song would dramatically change.

Once again, this is not communicated by a steady pulse from a metronome. Now, if you were rapping or singing or playing by yourself, you would almost undoubtedly use one of these, or another simple/compound meter, though you may not realize it. This is fine. But if you want to play with a group, especially if they're sight-reading something that you wrote, having the concept of bars coupled with time signatures is necessary.

  • Sight reading. You might be wondering why we can't just write out which beats are stronger without measures, and technically, we can. It's just really hard to read. Bars break the information down. It's much easier to feel measures than it is to theoretically know that certain beats are stronger than others. In a way, when playing as a group, nobody's really thinking that hard about measure, measure, measure, but counting becomes a lot easier when the numbers stay smaller.

  • Rehearsal. In orchestral settings, rehearsing one long stream of music would be quite challenging. First of all, if you got lost, it would really suck. Second of all, there's a lot of stop and go in rehearsals, and having measures as reference points, which give each beat their own unique feel in relation to the others (more having to do with meters) is profoundly useful. Thirdly, conducting is a lot more helpful when the conductor can show each beat in a measure by waving his hands in a different direction. For our 4 beats example, the conductor might show

DOWN right left up

With measureless music (which, actually, does exist) this isn't an option.

At the end of the day, measures are descriptive of the way we hear music and rhythm. They are also helpful for studying music as a group or even an individual because they allow places of reference.


Music is counted in beats, it is also counted in bars. Count a march - Left right Left right, One two, One two. Now count a waltz - One two three, One two three. That is why we sometimes group the beats in twos, sometimes in threes.

(Other bar lengths are also used, but they lack similarly neat illustrations.)

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    I'm confused by the same person providing this answer and criticizing another answer as being less useful to a "musically illiterate rapper" (a characterization that is unfair, unnecessary, and borderline on the 'be nice' policy, at best). Clearly this answer was not written with the "musically illiterate" in mind, why should any other answer be? – Todd Wilcox Apr 23 '18 at 1:52
  • @ToddWilcox I appreciate your comment very much. that said, I'm not offended by his comment as I'm illiterate in music by design. I don't read or write music and will never do so as I prefer everything by ear. I know about 80 songs now and working on them in all different keys and doing everything by ear and by theory I learn on this site. reading music I found limits me. – foreyez Apr 23 '18 at 15:40
  • @foreyez I was interpreting "illiterate" in the figurative sense of "doesn't understand anything about music theory", not in the literal sense of "the only missing knowledge is how to read or write music". I guess your attempt at learning theory without reading music explains the difference between the two answers, since this answer does not include any notation. But now I'm confused about why Mr. Payne would criticize the other answer since until your comment, there was no content in the question or your profile indicating you have no intention of ever reading music. – Todd Wilcox Apr 23 '18 at 16:02
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    @GalacticCowboy it's a sincere question because bars are used in DAWs. So I guess in a way I am writing music. but I was talking about not wanting to write or read traditional sheet music. mccartney didn't either. – foreyez Apr 23 '18 at 20:19
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    @foreyez - picking up on your first comment connected with this answer. I'd argue that those 'limits' are not being looked at properly. You have 80 songs. Each one, using your tactics, has/had to be 'learned'. What I try to get across to students - and now to you - is that when one can actually read music, the whole process of new stuff is incredibly quicker. In fact, there's no need to 'learn' any more stuff. I work in a couple of bands that will get the charts for a new song, and simply read it - usually note perfect. Think of the time saved by everyone here. O.k., we can go over bits >>> – Tim Apr 25 '18 at 6:55

Bars also make it easier to find and communicate reference points :

"Let's start again on bar 34"

enter image description here

Someone might count "1…2…3…4…" of bar 33 and everybody in the band will know exactly which note they should start with, and when to play it.


You'll actually find that more often than not, bars then occur in multiples of 8. Music is structured by rhythm. Where it gets interesting is when stuff works "against the beat" but just cannot escape it. Usually this works by having a "rhythm section" establishing the framework that melody instruments (or voices) then move comparatively freely in without losing their reference.

It's also common for the rhythm section to change harmonies on dependable positions within the meter.

By the way: most dancers would be pretty unhappy not having larger structures than single beats since it makes getting into a dance's meter and impetus gain and arrest much harder to work with if you don't have anything to depend on.


When the music is a song set to words, the accentuation implied by the bar lines is usually closely related to the rhythmic meter of the lyrics. For example:

enter image description here

We all know that this is stressed as

God save our gracious Queen / Long live our noble Queen

But it would be quite possible to set it to a different tune as

God save our gracious Queen / Long live our noble Queen

and this would need different bar lines to reflect the different stress in the music.


It's understandable that rap might not be as dependent on a division of beats into bars as other types of music. Rap can flow a lot more freely, and the words might or might not be arranged in phrases, verses or stanzas of the same length.

In other types of music the way the emphasis and phrasing are repeated is more important. In some cases there is a relationship between the music and the dancing that was popular at different times. A waltz is a dance step that repeats the same three steps over and over again, and the music that was played for a waltz did the same thing, repeated three beats over and over again. Bars were a way of keeping those three beats organized. Everybody danced the same three steps and the music helped them keep together.

So, while some types of music might not need such a strict structure, others are dependent on it for their identity.

  • 12-bar blues classics disagree with the "blues as we know it" part of this answer. – Mathieu Guindon Apr 23 '18 at 17:26
  • Correct, and thank you - I was trying to make it simple, but was too simple for the blues experts. – dwilli Apr 23 '18 at 17:29
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    I don't know if that's why the answer was downvoted, but: it's considered good behaviour in this site to edit a post if a clear problem has been pointed out in the comments. Blues really is not “usually” organised into 16 bars at all but into 12. Also, I think Blues is a bad example to begin with because it was originally played in a very free manner that often didn't exhibit much of a bar structure at all. (Conversely, rap actually tends to stick to a very strict underlying rhythm as far as I know, which isn't much though.) – leftaroundabout Apr 25 '18 at 15:17
  • Cool, thanks for the tip @leftaroundabout! – dwilli Apr 25 '18 at 15:58

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