Originally Posted by: zmirlinazim

Can someone explain why we have two notations for semitones when you could do the same with just one? For example, if D sharp and E flat are the same note, why not just use one notation?

This tutorial covers natural & accidental notes & how the musical alphabet is organized on the guitar fretboard.

https://www.guitartricks.com/tutorial.php?input=1136

The musical term for 2 notes with 2 different spellings is enharmonic.

The reason for 2 different possibles names for accidentals (sharps & flats) is to create perceptual convenience & conceptual clarity. Whether we call a note sharp or flat depends on the musical context of the song being played.

The default setting of naming a scale or key signature is to only use each letter once if possible. So, the key of E major has 4 sharps.

E - F# - G# - A - B - C# - D#

Rather than:

E - F# - G# - A - B - C# - Eb

This skips the note D, uses E twice. That makes for potential confusion in written form, in music notation & when communicating.

Also rather than:

E - Gb - Ab - A - B - Db - Eb

This is all flats, skips a lot of letters, uses E twice & again makes for a lot of potential confusion.

Let's try using th E-flat! The first key that contains an E-flat is B-flat major.

Bb - C - D - Eb - F - G - A

As opposed to:

Bb - C - D - D# - F - G - A

2 D's in a row! No use of E! Potential confusion!

By using all the letters in order & a consistent system of accidentals we get perceptual convenience & conceptual clarity. So, when possible, we make all of the accidentals either sharp or flat.

Hope that helps!