The Players School deals in music not the instrument of application. Music applies to the bass as it does any other instrument. If you can hear and identify chords for example you can play bass in that situation. You do not need to be able to play them or use them, but at least be able to identify them. Even in a simple jam the ability to recognise the chord that a player uses lets you play( if even the root) the correct choice and gives you a clue where he may go next. You might even be able to offer some colour in you own choices that will let the other players work around what you are given rather than you trying to follow or keep up.... you are part of it and involved.