How to translate 乎 in classical Chinese texts?

Question

I know that 乎 usually expresses doubt and is sometimes translated using rhetorical questions. But is it always true? I am wondering how should it be translated in such a case: "而有以通乎性命之全". The full sentence is:

惟人也，得其形氣之正，是以其心最靈，而有以通乎性命之全

For the sake of clarity - the sentence is preceded with another one that contains the following statement: "然体有偏正之殊".

Answer 1

is it always true

no. only when 乎 is at the end of a verse, then it might be interpreted as doubt, rhetorical question, or guess.

http://dict.revised.moe.edu.tw/cgi-bin/cbdic/gsweb.cgi?ccd=hj97ow&o=e0&sec=sec1&op=v&view=0-1

in the verse

而有以通乎性命之全

"乎" means 於, a preposition (at, in, from, . . . etc).

惟人也．得其形氣之正．是以其心最靈．而有以通乎性命之全

i would suggest to interpret the verse as:

only the homo sapiens (惟人也),

get (得) the upright (正) body (形) & vital energy (氣),

therefore (是以), its (其) mind (心) is the most (最) divine; (靈)

and (而) depends on [such upright body and vital energy] (有以), [homo sapiens ] succeed (通) in (乎) the complete (全) life (性命)

have fun :)

Answer 2

乎者，非唯语气助词之用也，亦作介词，同“于”之义。 试看： 风乎舞雩[在] 叫嚣乎东西，隳突乎南北[从] 吾尝疑乎是[对]