What is the interval between the notes on the 8th and 9th frets of the same string?

The interval between the notes on the 8th and 9th frets of the same string is indeed a half step. In standard tuning, the notes played on adjacent frets represent a movement of one semitone, which is defined as a half step.

When you play the note on the 8th fret, you are playing a note that is one full tone (or two half steps) lower than the note on the 9th fret. This movement from one fret to the next immediately adjacent fret results in the smallest interval in Western music, which is classified as a half step.

Understanding this concept is fundamental for navigating the fretboard, as it allows you to accurately determine distances between notes and understand how they relate to scales and harmony. The relationship of notes on adjacent frets is crucial for building muscle memory and developing a strong sense of pitch on the guitar.