Ive already learnt the 1-7 patterns, been told each number is a step...
But thinks like triads and sevenths confuse me, I'm usually better off listening and improvising but with the project I'm working on at the moment I want to follow my guitarist to the exact. Is there anyway I could easily figure out what note I'd have to play if he is playing those 2 string 'broken' chords as he likes to call them.
First off, 1-7 is not all a step wise progress.
To clarify: A step (whole step, whole tone, whole) consists of two half steps (semi tone). SO...
1 fret movement = semi tone
2 fret movement = whole tone
Major/minor scales consist of 5 whole tones, and 2 semi tones.
Look at C Major: C(1/R) D(2) E(3) F(4) G(5) A(6) B(7) C(8/1)
-E to F is a half tone, and B to C is a half tone.
The step/half step pattern of a major or minor chord allows you to figure out any scale starting on any note.
However, there is more to a scale than just that.
If you are playing C Major, you will (for now...) only use those exact notes in the scale in your chord spellings.
A Triad is essentially playing every other note with the root being the 1st note.
C E G is a C Major chord. (C is 1, E is 3, and G is 5)
However, if you want to play G you play
G B D (G is the root of the chord (1) but the Fifth of the scale. This is a bit confusing, just wrap your head around it) Just look at it G...a(skip it) B(keep it) c(skip it) D(keep it)
I did a write up a little while ago. People have pointed out some errors, but I corrected most I believe. Just look at the beginning of the information to start to understand. The rest is probably a bit more confusing.
http://www.talkbass.com/forum/f22/fretboard-logic-via-intervals-scales-chords-your-one-spot-787175/
So, to address your question... If he is playing broken chords, it is hard to determine what chord he is playing. You can always just play the same notes as he does, but that can steer you into not playing harmonically. Its not necessary to play perfect harmony by any means, but it is certainly pleasing to the ears when you have the right collection of notes.
If he is playing A over D and you play A over that, you are not playing any chord because you are missing something. Let us say F (D F A is D minor). If your lead is strumming A and D several times and you are strumming A, there is no chordal quality as to what you are playing. If you were to play F you would be playing a first inversion D minor chord. If you were to play D you would be playing D minor in root position, but you would not have the 3rd. (The 3rd determines if a chord is Major or Minor).
Honestly, learn the chord stuff. It may seem like jargon, but it will help you so much better in the long run.
Give a man a fish and feed him for a day. Teach a man to fish and feed him for a life time.
Do not be lazy about it. Think it. Write it. Understand it.
*Not everyone needs to play by theoretical rules, but there are plenty of threads on here suggesting that knowing the rules is always beneficial over not knowing.