請問He's as honest as can be，當中的as ...as can be是什麼詞性?

He is as honest as he can be.
as ... as
前面的as是「指示副詞」，後面的as是「連接詞」。
後面的as所帶出來的子句是「副詞子句」，修飾前面的形容詞honest，表示是同程度的比較。

He is honest.
He can be honest.
上面兩者用as ... as連接，形成同程度比較的關係。

I am not as rich as I was.= 我不如過去那樣富有了。

as honest as=the same thing as, in manner;
=as honest as (he) can be
=Will he be as honest as "he" can be?
=Will he be as honest as "his" words;
=sure to be honest + as" he" can be;
=introducing a non-defining relative clause, the antecedent being inferred "He".
,a conjunction;
eg:-As honest as" he" can be, "he" is as good as a gentleman.
I can see-----s+vt
himself-------DO
as honest as "he" can be-------DO followed by an adj cl. introduced by as, or a clause introduced by as---as;"he" is to be understood.