My bass teacher told me I should clip my nails short for playing bass.
But when i play with my nails a little bit longer so they kinda scratch te strings it makes a much brighter sound to just hitting the string with the flesh of my fingers.
If I want a defined attack, I use a pick. Picks vary in material and thickness, nails don't. Most of the time I play finger style. This varies from barely touching the string to striking and releasing it. Sometimes I play the e-guitar of my son (yes some bassists do) and then it can be fun to hit the strings hard with the back of my nails, producing chords with an extra zing.
Yes, yes, yes, I play with my nails all the time. I have to because I'm also a guitar fingerpicker. Sometimes I wish they were short for bass, to inhibit that click sound, but all I have to do is roll off the highs or high mids to make up for it. No problem, and this way I have the best of both worlds.
Tell your teacher he is WRONG!! You try one way, then the other and decide for yourself.
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2001 American Series Jazz Bass / 1987 Jazz Bass Special
Markbass Little Mark III / dual 151P cabs / 121H combo
Picks vary in material and thickness, nails don't. 
Most of the time I play finger style. This varies from barely touching the string to striking and releasing it. 
Sometimes I play the e-guitar of my son (yes some bassists do) and then it can be fun to hit the strings hard with the back of my nails, producing chords with an extra zing.
