Naming intervals: 2nd, 3rd, 5th… – free music theory course

An interval is the distance between two notes. Played one after the other, it is a melodic interval (rising or falling); played together, a harmonic interval.

The number: count the letter names

To find an interval's number, count the letter names including both ends. C → E: C (1), D (2), E (3) → it is a third.

C →	C	D	E	F	G	A	B	C
Interval	unison	2nd	3rd	4th	5th	6th	7th	octave

M:4/4
L:1/4
Q:1/4=80
K:C
[CD]2 [CE]2 | [CF]2 [CG]2 | [CA]2 [CB]2 | [Cc]4 |]
w: 2nd 3rd 4th 5th 6th 7th 8ve

The counting trap: a third is not "three notes further" but "the third note, counting the first one". C-E is only two steps apart, yet it is a third. That is why an octave (8) plus a fifth (5) gives a twelfth, not a thirteenth.

Reading intervals on the staff

Odd intervals (3rd, 5th, 7th): line → line, or space → space.
Even intervals (2nd, 4th, 6th, octave): line → space or the other way round.
A third = "next line"; a fifth = "two lines further"; harmonically, a third looks like a compact snowman, a second like two note heads squeezed side by side.

This is how experienced pianists read: they don't decode every note of a chord, they see its shape.

At the keyboard: a fifth falls naturally under thumb and fifth finger of a relaxed hand (C-G). A third: fingers 1 and 3; a fourth: 1 and 4. Memorise these spans in your hand as well as with your eyes.