I agree - tonality is used in some pretty confusing ways. The way I think of this is that acutance is contrast in small areas of the negative and provides an impression of sharpness (i.e., how sharp is the edge in small details that cannot be measured with a spotmeter, for e.g.). I think of tonality as the shape of the characteristic curve (contrast in big areas that can be measured with a spotmeter, for e.g.) which determines what kinds of greys you will get from different parts of the scene.(posted 8143 days ago)Small changes in curve shape can make appreciable differences in the print. You can keep the same area of the subject as white and black in both developers, but if the curve shape is different, the midtones will be rendered in very different ways by the two developers. Many compensating developers, for e.g., provide added shadow and midtone contrast at the expense of highlight contrast.
Cheers, DJ.