Here's why:
* Schwa sound: The schwa sound is a very short, unstressed vowel sound represented by the symbol /ə/. It's often found in unstressed syllables.
* Supersede: The word "supersede" has two syllables: "su" and "per-sede". The stress is on the first syllable "su", making the vowel sound in the second syllable "per" a short "e" sound, not a schwa.
Therefore, the correct pronunciation of "supersede" would be "soo-per-seed", without a schwa sound.