Cadences

Music has commas, full stops and paragraph used in the same way as storytelling.  The term for phrase (sentence) ending is called cadence.

Cadence means return to the I/i chord from iv or V chord. The stopping position of music that does not make sense to listener will not be fulfilling. Audiences expect a certain closure.

Authentic (Perfect) Cadences - V/v to I/i

Plagal Cadences IV/iv to I/i. It is used to end a phase rather than the song because they do not sound decisive as Authentic Cadences.  

Deceptive or interrupted cadences is to resolve the V/v to any chord other than I/i. The most common ones are V/v to VI/vi. This is one of the weakest cadence as it makes one feels incomplete.  Other forms are V to  IV/ii/V/VIIl.

Half (Imperfect) Cadences stop at IV, iv, V or v and not resolved to I (thus half of the cadence).