In reality, The Bass RUNS the band, whether the other band members / audience know it or not. Popular music forms we take for granted originate with the invention of Opera through the influence of theory and practice the 16th Century lutenist & Experimental scientist, Vincenzo Galilei (Galileo's dad). The essential structure of this form (monody) has 2 voices at work, The Melody and the Bass. -- everything, all other instruments grow from there.
We should all have a good idea about the melody, that’s the part which carries the lyrics - but let me talk more about what the bass does - as musicians understand the bass.
the PRIMARY RHYTHM instrument -- setting tempo, meter articulation with a solid prep-beats and down beats
the PRIMARY HARMONY instrument -- harmony is built from the bottom up (i.e. a root position C major chord is named after the Bass pitch "C". Furthermore All of the instruments tune to the bass.
The Bass thus provides the single focal point in which all instruments in an ensemble lock in. It is the conductor.
[e.g. * When I play in orchestras, I keep one eye on the conductor as I represent the sonic representation of their baton. When I am on stage, I keep an ear on everyone. The drummer locks in with me and we create a pocket so that other instruments don't get lost. We keep the groove going steady on because that groove subliminally and overtly overpowers anything the higher pitched instruments are doing. Therefore they need to listen to the bass if they are off, cause I WILL NOT BUDGE as the groove is far too important. -- I will only change in a desperate situation such as if its clear they higher pitched instruments are totally lost ---or just don't get it (or are stubborn) ** A bass in the hands of a clumsy performer, the sonic space in the venue gets easily cluttered and the whole band suffers as if the sound engineer pressed the "suck" button.]
Functional Harmony is built upon the Bass. The Bass directs the harmony. - If the guitarist, keyboardist, horns and vocalists are outlining a C major chord with the pitches C-E-G; The bass can change the character. Making it strong and stable by playing a C; propel it forward by playing an E; or destabilize it by playing a G
The Bass- can change the meaning entirely by playing, for instance and A - which changes the harmony into an A minor 7. -- And this is just the start…