Why only 3 fingers?

Hold up your hand. See how much shorter the pinky is?

Now try laying your fingers over the strings so the pinky gets the 1st string. Lift your hand out from the face of the guitar, and make the picking motion with each finger in turn. See how the pinky picks 'up' while the others go sideways?

That's why. You won't be able to get consistent tone.

When you practice classical, the audience should never be aware of which finger is being used - and for the physical reasons you just saw, that's not possible with the pinky.

Flamenco players use the pinky for rasgueado, but that's downstroke.

Interesting question. I just did a google search on 5-finger picking style and turned up references to "1970s East Coast style" or something. Leo Kottke may have used five fingers. I personally knew a guy back in the 70s that studied Kottke and could do some of his stuff, but using all five fingers. I thought it was weird (it looked like wet spaghetti flopping around!), but he already had maximum dexterity from playing piano from, well...from a *real* early age.

Then there were several references to 5-finger style on autoharp. It's true about the ring and little finger sharing some tendon space, but with work, we've all been able to defeat that somewhat on the fingering hand, so there should be no reason to try it on the picking hand.

I didn't get to look at all the page hits from that google search, but there were some interesting sites about 5-finger and other picking that might be worthwhile looking into.

I'm trying to remember; harpists, not blues harp players, but people who play orchestral harps - do they use ten fingers? I keep trying to visualize it but all I'm getting is Harpo right now. :)

Three fingers and the thumb may be the way fingerpicking is mostly taught today, but I wouldn't call it traditional. In my part of the country the traditional way is to use the index finger and thumb only. I can pick pretty good with my index, middle and thumb. But I'm finding the traditional method very difficult.

Some years ago I'd met a guy who'd gone to college with Leo in Minnesota. He was one heck of a fingerpicker too... but with thumb and three fingers. There are some references on the web to Kottke using five, but I'm not sure that's what he does - or he may use the pinky just occasionally for a treble note to avoid strumming two bass strings with the thumb, as classical technique would do. So I dunno if he uses four or fve fingers (it sounds like he uses about 12 and maybe some toes, too!).

Harp players don't use the pinky. From Piston's "Orchestration":

The strings are plucked near their middle point, with the fingertips and the outer edge of the thumb. The fifth finger is not used.

It's true you can get beyond the tendon issues - keyboard players do it, but the attack is different... they're coming straight down, and can compensate for finger length by moving the hand farther into the keyboard. To equalize the finger stroke on the guitar, you'd have to rotate the hand up towards the thumb, so you'd be picking a much steeper angle along the string - maybe 10-15 degrees from parallel, rather than the nearly across motion (70-80 degrees from parallel) in 'standard' fingerpicking.

That motion would probably open up some new sounds, even if you don't use the pinky... more of a bowing effect than a plucking one. I recall reading an interview with Kottke 2-3 years ago where he talked about using the bare fingertips rather than nails to get a bowing sound - I'll see if I still have it around, and let you know if he talks about how many fingers get involved.

Thanks for the replies everybody. I've been working on using all my fingers for the past week. I guess I'll come and brag if I get anywhere. I like the fact that I can use plenty of distorion without worrying about unmuted strings, since I only have two (E and A: I'm just scooting my fingers down a string and putting my pinky on the high e). It's a little awkward to keep my fingers on the strings at all times, but I think I'll get used to it all right. I'm being stricter than I would be if I used only my more dextrous fingers; each finger stays on its designated string. That kills my speed, but, oh well. I'm getting an even tone, but I do angle my fingers a little more to do so.