Usual is an adjective. It modifies or describes a noun or condition (implied noun).
Usually is an adverb. It modifies a verb -- an action. Adverbs "usually" end in ly. Think of an adjective and you probably add "ly" to it to make the adverb for that adjective.
So usual and usually have different functions, and thus are used differently in English.
The first version of the sentence is correct. It is not correct to say "As usually" in the second example. The second example can be made into proper English by adding a verb next to "usually" for immediate modification. So it could be written, "As usually happens, he forgot ...." and that would be okay.
The example given is kind of hard to work with because it also uses the word "As", which itself has a lot of slightly variable meanings (read more). In this example given "As usual", As roughly translates as "In the manner that is".
Usually is an adverb. It modifies a verb -- an action. Adverbs "usually" end in ly. Think of an adjective and you probably add "ly" to it to make the adverb for that adjective.
So usual and usually have different functions, and thus are used differently in English.
The first version of the sentence is correct. It is not correct to say "As usually" in the second example. The second example can be made into proper English by adding a verb next to "usually" for immediate modification. So it could be written, "As usually happens, he forgot ...." and that would be okay.
The example given is kind of hard to work with because it also uses the word "As", which itself has a lot of slightly variable meanings (read more). In this example given "As usual", As roughly translates as "In the manner that is".
