I don't think I ever said "tune by ear onstage"...
Also....I strongly disagree with you. If you are unable to tune your instrument by ear, that to me tells me that you lack the ability to discern a "right note from a wrong note".
I'll even go out on a limb and say guys that know how to tune by ear are better musicians than those who can't..
It works two ways. I don't want to hear anyone tune up on stage, by ear not even myself. The other should not cancel the other one out. You should be able to do both. Don't STRUT and BRAG and say that you MUST TUNE BY EAR prior to any song. The audience don't want to hear it, I don't. However, when sharing the stage with acoustic instruments that can't be tuned, you must tune by ear, or adjust your tuning apparatus to that one. Say, ANY acoustic piano, or grand piano, or vibraphone, marimba or such instruments which I've played to. If a vibraphone or marimba clashes with the acoustic piano then you're up in sh*t creek. You can't do anything to those on the spot, but if you know this in advance to the gig, you'd better check out the pianos tuning first. But if all else fails, you tune up to the piano and you just have to do that by ear.
The thing is, WHEN YOU PLAY you should be aware of that YOUR instrument can go out of tune while playing, AND ADJUST IT WHILE YOU'RE PLAYING. And if you can't, do not carry on playing, shut the f up and reach for your tuner, and tune silently and let the others of the band carry on playing. If it happens during a solo, and ONE string goes otu of tune, try - on the spot - to carry on the solo ELSEWHERE on the guitar, otherwise turn silent. If I discovers on bass, it's no big deal shifting positions, since very rarely a bass goes out of tune during a song, I've taken care of this beforehand to make tuning stable. I even get picky that if I use a drop D tuning, in one song, I discovers that after a while the drop D starts to drift upwards again, during the song, and goes
slightly out of tune. I stop playing that string or reach for the tuner (on the haedstock that is) to fine tune it. It it goes to flat, I'll just bend the string a tiny bit when fretting to bring it up again. No big deal.
The limb you're going out to, I am with you. I would go out and say that people can't JAM WITH OTHERS if they can't tune by ear, or really, hear when they themselves or someone else is out of tune. Jamming requires a lot of hearing the others in the band. And react accordingly within a split second.
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The important thing here, is not being able or able to tune to ear, or without a tuner, but hearing WHEN YOU'RE PLAYING if you're going out of tune or not. If push comes to shove, all worlds famous guitarists, legendary have a pitch problem and not hearing whenever they BEND A NOTE while soloing they bend it up too sharp. All those legendarys, Clapton, Beck, Page. Only a few of the anglo-saxians hard rock guitarists, from the blues-rock school posesses this very rare treat. Believe it or not, but how much I dislike Yngwie Malmsteens music, persona, on stage antics, and playing style, I've never heard him bend pitch out of tune. Same with late Gary Moore, which was one that could play in tune. Peter Green had bends in tune, and on top of that could vibrate the note without going out of pitch. Jeff Beck not. The guys in Umprheys McGee - the kings of improvised rock these days - can't bend in tune, they bend up too sharp, especially when playing live. I've heard - even - Steve Vai do this early on. Eric Johnson not, Steve Morse not, and actually Ritchie Blackmore not. Robin Trower has these assets too, not bending too sharp. Slash definitely not. Sour all of the time. Jeff Healey could bend to kingdom come without ever going out of tune, as well as Dickey Betts. But the others, no matter how much their guitars were intonated and was in tune perfectly they could bend up strings and keep in tune.
And the younger guitarists learn from their licks today. Inebriated or not.
And we haven't even started to talk about gtrds who press too hard (brought up on acoustics) and press
sideways some strings within a chord, just to get a firm grip of all frets on all strings. Occurs mostly on guitars with too low frets on. Sounds like torture to my ears, and it's no point in having to tune up any guitar at all in that case.