Hello!
I am training to play simple bass line on basics chords progression.
I started with C | Am | F | G
I want also to use a pentatonic scale.
Because the song is in C, I take C major pentatonic:
https://www.guitarscale.org/bass/c-pentatonic-major.html
But I have a problem when I have to play the F chords because… F is not in the scale.
Is there something I misunderstood ?
Thanks!
Well, don’t let a rule (or scale) limit you to what you can play! Trust your ears!!
In any case, you should be good with ALL notes from the C major scale over ALL of these chords as they are all diatonic to C major.
So, yes, F may not be in the C major penta scale, but it’s in the C major scale.
You’re good 
As Wooten the Great once said: “It’s the wrong notes that makes things interesting”. The rules, much like the Pirate’s Code, are more like guidelines.
Even if you’re sticking to the pentatonic scale for the majority of it, a little chromatic action here and there as a walk up or flourish will take it from basic to…uhm…bwoah.
Great question! That shape works over any major chord, so another option is to switch to F major pentatonic when you get to the F chord for a stronger sound. You can just slide the same shape up 5 frets. The 5 notes starting with F are also in the C major scale, so it all works.
Thanks for the idea, I find it amazing that C, F and even G have the same notes in major pentatonic. It really is magic!
I’m not sure I totally agree. I don’t mind that rules can be twisted, distorted or ignored when you reach a certain level of mastery, but since I’m still in the learning phase, it doesn’t hurt to understand how “it works”.
I’m not the kind of genius who, like Picasso, knew how to draw perfectly at the age of 6 and then spent his life reinventing ways of painting.
One of the “rules” is to know the rules before you break them. It’s the same in photography, one of the rules is to not put the subject in the center of the frame and use things like the rule of thirds… But sometimes you want to emphasize symmetry and you do want to put the subject in the center.
Victor wooten says a lot of things to demonstrate concepts about music but they’re usually only true in certain contexts. “There are no wrong notes” is not always true in all cases, all the time, because there definitely are wrong notes… Even in Jazz
Van Gogh only started his art career at the age of 27 and only it only lasted for 10 years. He produced around 2100 works including almost 900 paintings. He spent the first several years developing his techniques and did most of his paintings in the last few years of his life. Not everyone is a prodigy 
Fully understood!
This is where scales and melodies and scales and bass players have to go to different sides of the room.
If you were a noodle-y guitar player playing solos or coming up with a melody, the simple approach to play something nice over that chord progression would be:
Play things that you think sound good using just the C major pentatonic scale.
It wouldn’t sound perfect all the time (you’d still miss the F, for example) but it would sound over all very good - as a melody - over those chords, and you’d avoid hitting really bad, sour notes.
But!
You’re a bassist.
So for us, we can’t drop something light and shimmery over the top of the structure that will be shiny and nice, but has no real connection to the structure of the song.
You have to start at the bottom - the foundation.
So your bass line has to start with root notes on each of those chords.
Once you know the root pattern and can keep it perfectly and have a nice groove going, if you’re looking for other notes to add, the other notes have to fit inside each chord you’re on.
Unlike the guitarist/melody maker (who can ignore the underlying structure a bit so long as their notes sound nice and connect to the melody and key), all of the bass notes have to connect to the structure, which is the chords.
So the notes you play during the “C” part of the playalong have to connect to C.
If you’re adding pentatonic scales to embellish the bass line, the scale has to align to the type of chord. So, if it’s a C major chord you’re playing to, the bass line should be based around the C root note, and you can add notes from the C major pentatonic.
For the next chord, your entire world shifts, because the foundation is building from a new sound: the A minor.
You have to move to the A root note. If you want to embellish the bass line with a pentatonic scale, you have to add the notes from A minor pentatonic - because that’s the sound that matches the chord.
When you move to F, you have to move the bass to the F root note.
If you want to embellish the bass line during the F chord, you should use the F major pentatonic scale.
Same for G (starting from a G root, and using the G major pentatonic scale).
Using that basic guideline will give you a good bass line, will use scales appropriately, and will - hopefully - explain why you can’t just play C major pentatonic the entire time as a bass player.
Lemme know if this helps!
This is such a common and confusing thing, and I have been on a quest to try and make this more understandable lately with my writing and students!!
Best of luck to you!
Thanks for your detailed answer.
I crystal clear now.
Thank you for explaining this, @Gio . A big puzzle piece just clicked into place in my mind.
I had previously read that for improvising, you could use the pentatonic scale corresponding to the key you were in, and you used that over all the chords in the song. But this is the first I’ve heard that this is just for the “melody side of the room”.
I had never realized that the pentatonic scales built on all the scale degrees (except the diminished) were diatonic to the key. Assuming the pentatonic scale has the same major/minor quality as the corresponding diatonic chord of course.
This is kind of amazing!
Hooray!
You made my heart happy with this! So glad it helped.
just found this thread whilst researching modes believe it or not, but felt the need to comment 
i too was reading from the top thinking ‘noooo, surely thats not right’ until i read @Gio’s answer which is where my mind settled as thats what id thought all along. i think 
so can i just confirm my own thoughts (and that theyre aligned with Gios please)?
chord progression of I-vi-IV-V would have the pentatonic notes of I (C,E and G), then vi (A, Cb and E), then IV (F, A and C) and finally V (G, B and D) before returning to C?
i really hope so
thanks
Just to be precise those are normal diatonic triads (not limited to Pentatonic).
Diatonic - made up of notes within a scale
Pentatonic - a scale with 5 scale degrees
incorrect - the vi chord of C major is the A minor triad (A, C, E)
sorry, i meant triads not pentatonic, apologies.
and also yes, i should have looked at my fretboard rather than trying it in my head. theres no such thing as Cb anyway, im an idiot
thank you
@howard beat me to it, but yes - you’ve got the right idea, and all the notes were right.
I can see why you said Cb, because you know that the chord is minor, and you know that minor chord have a flat 3rd.
So, if C is the third of A in this key, you flatted it.
That’s the weird thing about our music jargon, and the cool thing about diatonic chords.
In any key, there is a mix of major and minor triads without doing any changing of the notes in the key signature.
The vi chord is always minor in a diatonic key signature, so you don’t have to change anything. It’s already changed.
This is deeper down the theory rabbit hole, but it may help to clarify some terminology.
A minor third is also called a flat 3rd.
It is referenced most often as a half step below the major third.
Another way to reference both of these is by counting the half steps (or frets for us) between the starting note and the second note.
A major third is 4 half steps away.
A minor third is 3 half steps away.
Thinking of the distances in terms of half steps can really help when you’re in a major key, but then there’s a diatonic minor chord, and you need the minor arpeggio, and things start to get major-minor jumbled in the brain.
Or maybe I just extra-jumbled things.
Anyway, happy to clarify, and I hope this helps!
It starts to get really cute and really jumbled when you learn to start walking around by alternating major and minor third intervals.
For people learning theory on bass this is likely a brain breaker