[sampo]

The music tradition sees the notes rather as intervals between two notes.

C to the same C is "unison" (You may need to instruments to play two identical C notes at the same time.)

C to C#/Db (this note has two names) is "small second"

C to D is "large second". And so on.

C to the next higher C is "perfect octave".

So if we take the C major scale, it has 7 different notes. But if we also include the next higher up C, you can pair the base C with 8 different notes, when we include pairing with itself, and pairing with the higher C. When you have two instruments playing, these are the pairings you can make when you play two notes at the same time.

https://en.wikipedia.org/wiki/Interval_(music)#Comparison

[chuchana]

> C to the same C is "unison" (You may need to instruments to play two identical C notes at the same time.)

> C to C#/Db (this note has two names) is "small second"

While C# and Db are the same note (in equal temperament [1]), the intervals C/C# and C/Db have different names: C# is called 'augmented unison' [2]. For the name, you start from the basic interval (e.g. C/C) and apply the accidentals (# or b) [3].

[1] https://en.m.wikipedia.org/wiki/Equal_temperament [2] https://en.m.wikipedia.org/wiki/Augmented_unison [3] https://en.m.wikipedia.org/wiki/Accidental_(music)

[sampo]

This is an example of why the traditional approach to music theory can be cryptic for a beginner. After the Western music moved to well and equally tempered scales (starting from the early 1700's), the context in which there is a difference between C# and Db has disappeared. But we still use terminology and notation from 500-800 years ago.