History: What is the difference between phaser and flanger?

What is the difference between phaser and flanger?

• Flangers cause inharmonic frequencies, but phasers cause harmonic frequencies.
  The opposite is true.
• Flangers and phasers both primarily cause harmonic frequencies.
  There is a difference.
• Flangers cause harmonic frequencies, but phasers cause inharmonic frequencies.
  Correct.
• Flangers and phasers both primarily cause inharmonic frequencies.
  There is a difference.