Having looked at each section of 'Stairway to Heaven' in detail, now we can draw conclusions and address why it's one of the greatest achievements in rock history.

My answer to why it's so great is its organic development – the way the melody and harmony of the verses grow out of what came before, continuously blending old material with new material. This graph illustrates:

One aspect I've ignored so far is tempo. The song gradually builds speed, before winding down again at the end.

0:00-0:54 Introduction: 64 beats in 53.8 seconds = 71.4 beats per minute

0:54-1:48 Verse 1: 64 beats in 53.7 seconds = 71.5 bpm

1:48-2:15 Verse 2: 32 beats in 26.8 seconds = 71.6 bpm

2:15-2:40 Transition A 1: 32 beats in 25.0 seconds = 76.8 bpm

2:40-3:07 Verse 3: 36 beats in 27.6 seconds = 78.3 bpm

3:07-3:31 Transition A 2: 32 beats in 23.4 seconds = 82.1 bpm

3:31-3:57 Verse 4: 36 beats in 26.5 seconds = 81.5 bpm

3:57-4:20 Transition A 3: 32 beats in 23.0 seconds = 83.5 bpm

4:20-4:45 Verse 5: 36 beats in 25.5 seconds = 84.7 bpm

4:45-5:08 Transition A 4: 32 beats in 22.0 seconds = 87.3 bpm

5:08-5:35 Verse 6: 36 beats in 25.3 seconds = 85.4 bpm
NOTE: The measure that connects Verse 6 and Transition B 1 uses a fermata to artificially extend its temporal duration, which skews the numbers. To be consistent, I'm omitting that measure from this analysis.

5:35-5:56 Transition B 1: 31.5 beats in 20.1 seconds = 94.0 bpm

5:56-6:45 Solo: 80 beats in 48.8 seconds = 98.4 bpm

6:45-7:47 Verse 7
   6:45-7:27   [vocal]: 18 measures = 72 beats in 42.3 seconds = 102.1 bpm
   7:27-7:47   [instrumental]: 28 beats in 17.5 seconds = 96.0 bpm
NOTE: I'm again omitting the final measure as it uses another fermata, which skews the numbers.

7:47-8:02 Coda: freely (not in rhythm)

Here's the same information in the form of a line graph:

The seventh and final verse adopts the same (g) two-bar phrasing of the solo, repeating it 13 more times (for a total of 26 measures) with Plant adding vocals to the first nine phrases.

6:45-7:47 (D') Verse 7 (26 measures)
    6:45    (g)    |a G |F | “As we wind...”
    6:50    (g)    |a G |F | “Our shadows...”
    6:54    (g)    |a G |F | “There walks...”
    6:59    (g)    |a G |F | “Who shines...”
    7:04    (g)    |a G |F | “How everything...”
    7:08    (g)    |a G |F | “And if you listen...”
    7:13    (g)    |a G |F | “The tune will come...”
    7:18    (g)    |a G |F | “When all are...”
    7:22    (g)    |a G |F | “To be a rock...”
    7:27    (g)    |a G |F | [instrumental]
    7:32    (g)    |a G |F | [instrumental]
    7:37    (g)    |a G |F | [instrumental]
    7:42    (g)    |a G |F | [instrumental]

The final four phrases are instrumental and ritard the tempo, leading to...

Continuing the organic development we saw in verse 3, verse 5 retains the (d) harmonies while simultaneously introducing the new (e) melody.

4:20-4:45   (C) Verse 5 (9 measures)
   4:20   (d & e)   |C G |a |C G |a |   “If there's a bustle...”
   4:31   (d' & e)   |C G |a |C G |a |C G |   “There are two paths...”

Verse 3, like verse 2, contains two phrases. Those phrases are identical except that the latter is extended by a single measure (five bars long instead of four). Both reprise the (a) melody from the first and second verses, but with new (d) harmonies.

2:40-3:31   (B) Verse 3 (9 measures)
   2:40   (a & d)   |C G |a |C G |a |   “There's a feeling...”
   2:52   (a & d')   |C G |a |C G |a |C G |   “In my thoughts...”

This third verse cannot be called a new section because it brings back an old melody. But it also cannot be called an old section, either, because the chords are new. So it's half new, half old. This is a technique known as organic development because the music grows out of what came before, just like a seed sprouts and flowers. I analyzed the organic development of 'Good Times Bad Times' earlier. This is the same technique, but on a much grander scale.

While Verse 3 is the first time those (d) harmonies are used, they will be heard again six more times (two each in verses 4, 5, and 6):
   3:31   (d)   Verse 4
   3:42   (d')   Verse 4
   4:20   (d)   Verse 5
   4:31   (d')   Verse 5
   5:08   (d)   Verse 6
   5:19   (d')   Verse 6

 Verse 4 is identical to verse 3, just with different lyrics.

3:31-3:55   (B) Verse 4 (9 measures)
   3:31   (a & d)   |C G |a |C G |a |   “And it's whispered...”
   3:42   (a & d')   |C G |a |C G |a |C G |   “And a new day...”

There are two different transitions in 'Stairway to Heaven'. The first, which I call "Transition A", is heard a total of four times. The second, "Transition B", is heard only once.

I've blogged about both transitions before - Transition A was part of my rhythmic displacement series, and I compared the rhythmic instability of Transition B to The Beatles' 'Here Comes The Sun' in another post.

All four Transition As consist of four phrases, each comprised of identical two-measure harmony (a-D). What's different about the total 16 phrases (four Transition As x 4 phrases each = 16 total phrases) are Robert Plant's vocals. Five of those 16 phrases include the line "makes me wonder" while the remaining nine are instrumental. (NOTE: There are two phrases where he sings "Oh", but I'm counting those as instrumental.)

The final transition, the only iteration of Transition B, is quite different from Transition A, and particularly interesting.

5:35-5:56   Transition B 1 (8 measures)
   5:35   (f)   |Dsus4 |D |C |  |    [instrumental]
   5:46   (f')   |Dsus4 |D |C |G/B |    [instrumental]

But I've already considered this Transition B in a previous blog, so there's no need to repeat it here.

I've already written about the first verse of 'Stairway to Heaven' in my series on rhythmic displacement, so I'll consider it only briefly here.

The first verse is structurally identical to the instrumental introduction. Both employ four phrases, each four measures long, the first two of which are identical, the last two of which are comparable and so labeled (b) and (b'). Most interesting is that Plant's second verse ("There's a sign...") begins early, at 1:34, overlapping with the fourth and final phrase of the first verse.

0:54-1:48   (A) Verse 1 (16 measures)
   0:54   (a)   |a E/g# |C/g D/f# | FM7 |a |    “There's a lady...”
   1:07   (a)   |a E/g# |C/g D/f# | FM7 |a |    “When she gets...”
   1:21   (b)   |C D |FM7 a |C G |D |    “Ooo...”
   1:34   (a & b')   |C D |FM7 a |C D |FM7 |    “There's a sign...”

Part of me wants to label the third and fourth phrases as their own distinct section. I could see this as a bridge instead of part of the verse. But bridges are defined by contrast to the verses, and while there certainly is some contrast, there is also a lot of similarity.

The first four chords of the phrase in question (C-D-FM7-a) are the same as the last four chords of the previous phrases. The harmonic rhythm is faster (covering two measures instead of three), and the chords are all in root position (no inversions this time), but there is a clear and strong harmonic similarity.

​Now, there are many songs where the verses and bridges share strong harmonic similarities but there are other differences, such as melody, that distinguish the two sections. But in 'Stairway', there is also a clear and strong melodic similarity. While the first half of the phrase in question is different (“Ooo...”, shown below with blue notes), the second half employs the same pattern as the previous phrases. They even use the same lyrics (“and she's buying a stairway to heaven”, shown in red).

Verse 2 is half as long as verse 1, and it's identical to the first half of verse 1 (save for the lyrics).

1:48-2:15 (A') Verse 2 (8 measures)
   1:48   (a)   |a E/g# |C/g D/f# | FM7 |a |    “In the tree...”
   2:01   (a)   |a E/g# |C/g D/f# | FM7 |a |    [instrumental]

The reason for this abbreviation is because we've heard the (a)(a)(b)(b') pattern twice already (once from 0:00-0:54 as the intro, then again from 0:54-1:48 as the first verse). To avoid any threat of monotony, this third iteration (and every subsequent iteration) is curtailed to two phrases. This truncated second verse leads to the first transition, which I'll consider tomorrow.

Having completed the overview, we now turn to the individual sections for a more detailed look.
​
At their most fundamental, introductions set up what comes next. This almost always means the music heard in the intro will be heard again later in the song. And 'Stairway to Heaven' is no exception.

The instrumental introduction of 'Stairway' consists of four phrases, the first two of which are essentially identical and the second two of which are comparable.

0:00-0:54  (A) Introduction (16 measures)
   0:00   (a)   |a E/g# |C/g D/f# | FM7 |a |   [instrumental]
   0:14   (a)   |a E/g# |C/g D/f# | FM7 |a |    [instrumental]
   0:27   (b)   |C D |FM7 a |C G |D |    [instrumental]
   0:40   (b')   |C D |FM7 a |C D |FM7 |    [instrumental]

The (a) phrases are heard a total of six times: twice each in the introduction, first verse, and second verse.
   0:00   (a)   Intro   [instrumental]
   0:14   (a)   Intro   [instrumental]
   0:54   (a)   Verse 1   “There's a lady...”
   1:07   (a)   Verse 1   “When she gets there...”
   1:48   (a)   Verse 2   “In the tree...”
   2:01   (a)   Verse 2   [instrumental]

The (b) and (b') phrases are heard a total of four times: twice each in the intro and first verse.
   0:27   (b)   Intro    [instrumental]
   0:40   (b')   Intro    [instrumental]
   1:21   (b)   Verse 1    “Ooo...”
   1:34   (b')   Verse 1   “There's a sign...”

It's worth noting how both the (a) and (b) phrase are only used in pairs – they never once appear as a single phrase.

It's also worth noting how the (a) and (b) phrases are used together in the intro and first verse, but the second verse uses only the (a) phrases. We'll address why that is in a subsequent blog.

​We've already seen how 'Dazed and Confused' and 'Houses of the Holy' displace one beat (though in opposite directions), how 'When the Levee Breaks' displaces one measure, and how 'Stairway to Heaven' displaces by two beats and by an entire phrase.

Next and last in this series is a song that displaces half a beat: 'Black Dog', the initial track of Led Zeppelin IV (1971).

​In this case, a seven-note pattern lasting nine eighth notes... 

Lesser musicians might have repeated these musical ideas more or less the same each time. But Zeppelin, ever attentive to detail, found ways to subtly alter their music in a way simultaneously familiar yet different through rhythmic displacement. And that, I suspect, is one trait (of many) that separates the good bands from the great bands.