Hi, Eric. The four forms you cite can be used as verbs, and two of them, "aggregate" and "total" can also be nouns and adjectives. When they are used as verbs, "amount to" is followed by a quantity without any implication that it results from the addition of various factors (no plural subject is needed). That makes "amount to" different from "add up to", which alludes to the quantity following "to" being the result of adding two or more factors (that is why it needs a coordinated or plural subject). As to "total", if it is used as a verb (derived from the adjective "total", cf. below), it is approximately equivalent to "add up to"; if it is used as a count noun ("a (grand) total of ___") it refers to the resulting set itself. As to the original adjective "total" it comes from Latin "totalis", and this, in its turn, from Latin "totum" (= whole), and roughly means "complete". As to "aggregate", it is derived from a participle "aggregatum" (cf. below). If used as a verb, it means to "group" or "add" units or sets to a preliminary total or set to form a more comprehensive set. The result of the aggregation operation is an "aggregate", roughly a "group" (but also a "subgroup", to the extent it is added to the main group). As to adjectival "aggregate" itself, it comes from Latin "aggregatum", the past participle of "a(d)>g-gregare" = to add a head of cattle to the flock. As an adjective, it roughly means "added." The evolution is this: 1) Latin participle "aggregatum" > 2) English regular participle "aggregated" > English irregular adjective "aggregate" = added > 3) English verb "to aggregate" = to make x an aggregate of y > 4) English noun "aggregate" = the x aggregated, or the y resulting from the aggregation of x to a previous set. In the case of "total", the sequence is 1) Latin adjective "totalis" (from "totus/a/um" = whole, all) > 2) English adjective "total" = complete > 3) English noun "total" (resulting sum) > 4) English verb "to total" (= to make the total of ___ ). I hope this quick summary helps you understand the differences between those four words.

The words stated above are basically unanimous in nature. The differences of such words will be on the technicality of the sentences given. :)