  The traditional method of morphological classification, by visual inspection
of images of uniform quality and by reference to standards for each type, is
critically examined. The rate of agreement among traditional morphologists on
the morphological type of galaxies is estimated from published classification
works, and is estimated at about 20 %, when galaxies are classified into three
bins (E, S0, S+Irr). The advantages of the quantitative method of structural
classification for classifying galaxies in clusters are outlined. This method
is based on the isophotal analysis of galaxy images, and on the examination of
quantitative structural parameters derived from this analysis, such as the
profiles of luminosity, ellipticity and deviations from ellipticity of the
galaxy. The structural and traditional methods are compared on a complete
sample of 190 galaxies in the Coma cluster. The morphological types derived by
both methods agree to within 15 or 20 %, the same rate as among traditional
morphologists alone, thus showing that our morphological classes do coincide
with the traditional ones. The galaxies with discrepant types are mostly faint
(mag_B > 16.0), or have features typical of spirals, but which have not been
detected, noticed or taken into account by traditional morphologists. The rate
of agreement is also good for galaxies in a distant cluster (z ~0.4). The
structural method, gives highly reproducible results, never reached by
traditional estimations of the morphological type. Thus, the morphological
types obtained with this method should be preferred. The advantages of the
method are further demonstrated by new results on the properties of galaxies in
clusters.
