When jamming i always played over chord progressions in a certain key and played the scale that goes along with it. I've improvised with people doing this method. Today i was jamming with a potential band mate and he said he doesn't use scales or any kinda theory he plays by ear. I didnt know that you could just improvise by ear. Well we were trying to improvise but i didn't know what scales to use because that is just the only way i know. The chords he would play was all jumbled up like chords that didn't go together. How to i play with someone like this?
You can't jam with somebody who's playing random chords unless you know what chord he is going to play next. Tell him to learn some theory.
Well, good improvising is done by ear, not by playing random notes in a scale. Scales do help you with navigating on the fretboard, though.

I would suggest ear training. Learn to recognize different chords and you don't need to ask what chords people are playing. Without having a good ear, you really can't jam. Because jamming is all about listening to each other and reacting to each other's playing.

Your friend does play scales and chords. He just doesn't know the name of the scales and chords he is playing. And all that matters in music is the sound, not the scale names. But yeah, it could help if he learned some theory. But it would also help if you learned to play by ear. A good ear is the most important skill a musician can have. It is what makes you a musician. I mean, think about it. Music is all about sound. You need ears to hear sounds. If you don't use your ears, how are you supposed to play music? Sound came first, theory just explains those sounds.

You can't really not use scales or theory. Because they are always part of music. Your friend doesn't know theory as we know it, but he does know how music works by ear. Of course you can play without thinking about scales or theory. But they are always there. Theory can explain everything in music.

And the method you are using is right. Of course you pick the scale that goes well with the chords you are playing over. That's also what your friend does. He just doesn't know all the fancy names for what he is doing.
Last edited by MaggaraMarine at Nov 1, 2014,
Well, mostly everyone else hit it on the head. Good improvisation is done by "playing by ear." If you're friend is playing just random chords, and either of you has no idea where he's go next, there will be mis-communication and the jam will sound terrible.

When people actually do jam, they pick a key to play in and play that progression. For example, most players do a 12-bar blues in "guitar-friendly" keys like E, A, G, or D. Each person then will you their knowledge and solo over that progression. If you know the notes of that key along the fretboard, then you're more familiar on where some target notes are. But when you do improvise, you should try your ear as much as you can when creating lines.

Even if your friend (or anyone for that matter) doesn't know the names of every type of chord/scale, they should at least know common chord progressions and major/minor/pentatonic scales in every key. As long as they know the bare bones of theory, aural ability should help them the rest of the way.

Then again, I haven't had the chance to play with other musicians in like 1.50 years now due to work and school, so I can't give personal experiences. Even, if you want, you can improvise with backing tracks either found online or made by yourself if you're feeling creative.

I hope that I could help out and possibly clear anything up. I'm currently getting back into playing (seriously) myself after a few months. Just keep on playing!

There seems to be a bit of a recurring theme (in the gear forums as well) that guitar-playing friends are quite often full of it.
I've jammed with some musicians who are like that. It helps if you can get him to repeat whatever he is playing so you can figure out how you should play over it.