Intervals

If two notes sound different, one must be higher - the other lower.

The distance between the sounds is referred to as an interval.

The smallest interval is a semitone, on the guitar, one fret. Two frets or semitones make one tone.

The note immediately above C is therefore C#, the next D and so on.

On the guitar in the key of C major there are two frets between all of the notes excepting E and F and B and C. 

Interval sizes are determined by counting the letters from the lowest up. C to E is C,D,E and is therefore a third.

Any interval that is counted from the tonic of the major scale to another note in the scale is a perfect or major interval.

• If a major interval is reduced by a semitone it becomes a minor interval
  
  
• If a minor interval by a semitone it becomes a diminished interval
  
  
• If a major interval is increased by a semitone it becomes an augmented interval
  
  
• If a minor interval is increased by a semitone it becomes a major interval

Accidentals

Accidentals are symbols that represent a change to the pitch of a note, they can be sharps(#)

that raise a note by one semitone, or a fret, and flats (b) that lower a note by a semitone and naturals that return a note back

to its natural state. 

On the guitar the interval between B and C, E and F is one note or fret.

The interval between all other notes two notes or frets.