Is the following sentence passive? (context: referring to the second dictionary entry definition for the word 'spiritual')
This second usage of spiritual I do not approve of.
I believe that putting "I do not approve of" at the end places emphasis on "this second usage of spiritual" being the subject, as opposed to "I" being the subject. Do you agree with this? If so, is this a valid reason to use the passive voice, to change emphasis?
No: this is not passive voice in any way whatsoever:
This second usage of spiritual I do not approve of.
This is merely object–verb–subject (OVS) ordering instead of subject–verb–object (SVO). It is the same grammatical structure as saying:
I do not approve of this second second usage of spiritual.
The subject is still I in both cases: it does not change to usage just because usage happens to be in front. If I were an object, it would be me, and it’s not.
If you take a sentence like:
The dog bit the boy.
And reverse it with a tensed inflection of be plus the original verb’s past participle with by and the old subject as an object of that preposition:
The boy was bitten by the dog.
Then that is passive voice. Merely putting the object in the first position is not sufficient to be passive voice.
Although you need some more practice in classifying English verbs by voice, you have spotted one of the reasons to use the passive -- placing the subject first when the acted upon party should receive the emphasis:
The Affordable Care Act was passed by Congress in 2010.
Here the ACA receives first billing as the subject of the passive voice "was passed." The active form would put Congress up front, where it doesn't need to be since all laws in the US are passed by Congress.
There are other good reasons to use the passive.
When the actor is unknown:
Three people have been robbed downtown in the last week.
The robbers remain unidentified.
When identifying the actor isn't important:
Firefighters arrived at the burning apartment building at ten o'clock. Three people were admitted to the hospital for smoke inhalation.
Presumably somebody at the front desk did the admitting, but no one is interested in their particulars.
To disentangle syntax:
The resolution was supported by the mayor, who was elected last year.
This is better than the active-voice version, in which the mayor's election history separates him from his verb.
