by RonPurewal Fri Oct 03, 2008 5:52 pm
"fewer", as the poster above has said, applies to literal COUNTING of things. if you can't count things, one, two, three, ..., then you don't want to use "fewer" for them.
"lesser" describes the degree of some quality or state. in fact, the most common noun modified by "lesser" is "degree". "LESSER" IS NOT THE SAME THING AS "LESS", which is a word that describes uncountable quantities of stuff.
there are several contexts in which "lower" can be used; which one did you have in mind? it could refer to quantities, for instance, or it could literally refer to vertical space.