  This paper describes a framework for studying galaxy morphology, particularly
bar strength, in a quantitative manner, and presents applications of this
approach that reveal observational evidence for secular evolution in bar
morphology. The distribution of bar strength in galaxies is quite strongly
bimodal, suggesting that barred and unbarred systems are distinct entities, and
that any evolution between these two states must occur on a relatively rapid
timescale. Bars' strengths appear to be correlated with their pattern speeds,
implying that these structures weaken as they start to slow, and disappear
entirely before the bars have slowed significantly. There is also tantalizing
evidence that bars are rare beyond a redshift of z ~ 0.7, indicating that
galaxies have only recently evolved to a point where bars can readily form.
