"not only ... but also ..."
"not only ... but ..."
"not ... but ..."
the difference here is strictly one of MEANING.
the first two are pretty similar; the last one is TOTALLY different.
(1) "not only ... but also ..." is used to refer to two descriptions thatREINFORCE each other (i.e., both have the same connotation -- two good things, two bad things, two helpful things, etc.), but are fundamentallyindependent.
this drug is not only an alertness aid, but also an antidepressant.
--> "alertness aid" and "antidepressant" are TWO GOOD THINGS that have basically NOTHING TO DO WITH EACH OTHER.
therefore, "not only ... but also".
(2) "not only ... but ..." is also used to refer to two descriptions thatREINFORCE each other, but it's generally used when the second description EXPANDS or GOES BEYOND the first.
ryan not only competed in all the events, but won first prize in three of them.
--> note that "won first prize in three of [the events]" is an EXTENSION of "compet[ing] in all the events". these are not independent.
the above difference between (1) and (2) is subtle, and is therefore not terribly important. however, you MUST be able to tell those from the next one:
(3) "not ... but ..." is used when the FIRST thing is EXPECTED, ASSUMED, or PREVIOUSLY THOUGHT, but is REFUTED / CONTRADICTED / DISPROVED by the SECOND thing.
the snacks known as "french fries" were invented not in france, but in belgium.
--> the initial assumption, which is refuted, is that french fries are from france.