I Twittered up a minor storm a while back by saying:
I don't fetishize the 50mm lens. It's often too long on APS-C sensors.
I don't decry the points that anyone made about choosing the 50mm lens as a first additional lens for a new photographer. John Gruber's characterisation of this lens as "the best deal in photography" is perfectly appropriate. It is by far the cheapest route into the sub-f/3.5 lenses. It's wonderfully small, light and sharp. I still own one myself and it was, indeed, my first additional lens.
There are two parts to most discussions about this lens: its fast aperture and the fact that it is a prime lens. Now, don't get me wrong, I adore my prime lens kit of the 50mm f/1.8, the 85mm f/1.8 and the 100mm f/2.8 Macro. I'm not anti-prime lens in any way at all. That's not the point. The point I want to explore is why people believe and assert that a prime lens will make you a 'better' photographer, for some value of 'better'.
Firstly, lets define "better". What does it mean to become a better photographer? I'll develop a positive definition in a moment, but first think about what the difference between the good photographer and the great photographer is not: in the age of autofocus, TTL metering and the various common exposure modes, the difference is not found in a photographer's deep understanding of which setting to use.
What sets great photography apart from good photography is not the technical at all, it is nothing more or less than the impact of the photograph on the viewer. Technical mastery of the camera merely separates the acceptable from the unacceptable, and could even be argued to be orthogonal to the impact of the photograph.
That said, why advocate prime lenses for beginning photographers?
Modern cameras provide several axes of fiddling - shutter, aperture, ISO and zoom setting are just the Big Four - and a prime lens teaches the new photographer that one can indeed produce excellent photographs without having to consider every one of these axes for every shot. By mounting a fixed lens, you remove one axis of fiddling - the focal length to use. To take this line of thought a step further, consider making heavy use of your camera's Program mode. Then, all you have is your camera position and your sense of timing to play with. That's really stripping photography back to its beating heart.
What the prime lens really teaches you is this: constraints lead to creativity. There is much more to think about in photography than just shutter/aperture/ISO/zoom. Instead think about where you put the camera. How near do you go, how high or low? How are you arranging the elements of the picture to communicate with the viewer?
Where I differ from some photographic commentators is the noble notion that whatever was good enough for Robert Capa or Cartier-Bresson should be good enough for you and I. I strongly disagree with any claim along the line that prime lenses are somehow a purer expression of photography than zoom lenses. Yes, we all love elegant equipment and, heaven knows, the Leica M8 is burning a hole in my heart right now. However, the existence of historically important photographs taken with prime lenses only serves to disprove the counter-claim that zoom lenses are a necessary precondition to good photographs. It doesn't prove anything much about the virtues of prime lenses.
My own opinion is that learning to handle an ultra-wide-angle lens in the 10-25mm range is an even better photographic education than a prime lens, but that's another post for another time.