Minor key: Sad music is often written in a minor key. Minor keys are darker and more dissonant than major keys, and they can create a sense of unease or foreboding.
Use of dissonance: Dissonance is the use of two or more notes that sound unpleasant together. Dissonance can create a sense of tension or unease, which can be effective in conveying sadness.
Repetitive melodies: Sad music often features repetitive melodies. This can be because repetition can help to create a sense of melancholy, and because it can help to emphasize the emotional impact of the music.
Use of instruments associated with sadness: Certain instruments are often associated with sadness, such as the violin, the cello, and the piano. These instruments can be used to create a sense of pathos and emotion.
Use of lyrics that express sadness: The lyrics of sad songs often express feelings of sadness, loss, or regret. This can help to reinforce the emotional impact of the music.