I am catching up on a lot of Beginner topics after neglecting them for too long due to other tasks at hand.
So here is a catch-all with lots of quotes and comments.
John - Justin repeatedly stresses through the Beginner course the necessity of keeping your thumb down behind the neck to help develop vital strength in your hand and fingers that will be needed as you progress. As Justin is not a beginner he often (and he can’t help it) defaults to a grip with thumb up higher, perhaps even a little over to mute the low E string. But he does try to check himself and restate that thumb behind is best if and when he catches himself not doing that in the video.
Good advice.
100% on that.
Yes, this is the advice Justin tries to mention whenever it is needed. He may occasionally forget to say it in a video lesson.
Good question, here is my take.
Muting the low E is not the primary aim of making the chord. The primary aim is all to do with correct and accurate finger placement and clean sounding fretted / open string notes. If there is a string not part of the chord (low E in the C chord for example) then option 1 for beginners is to try to focus on not hitting that string in the strumming. But if option 1 is followed unsuccessfully and the low E string is accidentally strummed then no sweat, it is not a big, big deal. Option 2, but one to consider only when more confident with finger placement etc is a secondary aspect of seeking ways to backup the option 1 (don’t hit the low E string) method and that is to try to mute the low E string. But it is not easy and is not an intrinsic part of learning to play the chord from the first step. It can come after if and only if a beginner has got to grips (excuse the pun) with the actual substance of the chord itself. The thumb behind facilitates and allows the fingers to form the chord from that first step so is not a detriment nor is it less than optimal.
Can you achieve the same result by slightly altering the guitar position and angle of the neck?
Ah … behind is good, pointing to the headstock is not.
Your fingers will develop more stretch over time (are you using the stretch exercises for beginnres?) and angle of neck and fingers makes a difference.
It is not a question of pressing harder - you do not want to apply more pressure down on the string as it will sound sharp, it is about a micro adjustment to your finger placement.
ps
The action of your guitar looks high. See how far above the fretted note the open E string is sitting? That will be adding to the difficulty of muting with a small touch. It will be adding the difficulty of everything.
Look at this image. I have added some white arrows to show what I mean. Some small adjustments to your neck relief (truss rod) and your bridge & saddle heights will help lower that. If you’re unsure, ask in the Gear section.
If the muting is achieved to the detriment of the actual chord formation then do not worry about it. It is secondary. Chord formation takes 100% precedence over add-ons. Once you improve your chord formation the muting will come easier.
Good advice all round. It does look a little like your fingers are on top of the fret wire but I assume that is optical illusion otherwise your notes would not sound clean. They are also somewhat perpendicular as @jjw observes.
When a song (or your ears) want a Cadd9 rather than a regular C then all is good.
But on many occasions you will want and need regular C so do not neglect it and leap to something almost the same that you find easier.
Andre, your fingers 2 & 3 are still a little too perpendicular to the neck and your 4th finger needs to be hugging the others much closer - not pushed far away like a lonely child.
Try rotating the wrist of your fretting hand a small amount. In the pic above, the rotation would be to make your three fretting fingers also rotate a small amount anti-clockwise as we look at them from the front, angling them into the frets more. See the screenshot from Justin’s video lesson posted here.
A long way down in a secondary position.
Making the chord, good formation and sound clean is #1 priority above all else.