Cliff Williams is more adding the third. You can basically play any note in a chord and aren’t limited to playing the root, but I suspect you’ve already figured this out. A lot of bass lines are root/fifth or root/fifth/third unless you’re playing walking bass lines, which will typically walk up and down the neck outlining the chordsYeah. I was talking in a general sense. And I've been known to comp percussion with other guitar players (Acoustic) when they tend to lose the beat. SO following the idea of the thread, do you have any suggestions on technics for Bass as far as percussion. I'll assume Slap Bass is a good example of that, which is a technique I know nothing about. I'm also interested in hearing about any non standard chord tones to play on Bass given a specific guitar chord. Say for example an A note on the G chord for the 9th sound. I remember something about that type of deal with Cliff Williams somewhere. I like to think that Bass has more in common musically with guitar and other strings but rhythmically more in common with drums. But opinions vary.
As a tip, most guitarists play ascending licks. Bassists on the other hand will often (but not always) do descending lines and resolve on the root.
As for techniques, it’s not so much about slap as it is about plucking, muting and note duration. With fingerstyle, most guitarists go for sustain and pluck the top of the string. With bass, pull through the string so that the pad of your finger mutes it momentarily between notes, like the beater hitting a drum. It’ll give more a more percussive thump instead of a drone with a better separation between notes and (potentially) a deeper groove. Standard wisdom is to strike on the kick and mute on the snare, but once you get a feel for that you can experiment with pushing and pulling the beat.
If you have any experience playing drums or a good ear for it you can start to play fill patterns. When you and the drummer are locked in and playing the same fills the fills gain more power.
As for guitar, I don’t generally try to lock in with the guitar players and most of the time I don’t even know what they’re doing. I spend most of my time locked with the drummer laying the foundation and driving the song using passing tones to connect the chord changes together. I play most of my counterpoint off the vocal. Sometimes I’ll play off or double the lead guitar. It’s pretty rare that I actually double the rhythm guitar, and that’s usually only for a few bars to emphasis what he’s doing before switching back to the drums.
That said, that’s how I play. Plenty of other people have their own (equally valid) way of playing.