Today I have met following new question, for which I tried to find clear answer but failed; in non-restrictive relative clauses can both relative pronoun and ‘be’ in a passive clause can be left out?
1. I found out the above rule can be applied to the relative clause in which the antecedent of relative is acting as a subject for whole sentence as follows;
using a past participle in a passive clause:
* "The theft, discovered by the manager, was reported to the police", which could be rephrased as:
* "The theft, which was discovered by the manager, was reported to the police"
This kind of post-modification of the noun phrase is generally non-restrictive so the defining or restrictive forms without commas do not provide the same sense.
2. Yet, I haven’t heard with what kind of grammar rule ‘which was’ in this sentence can be left out, while I think that since non-restrictive relative clauses usually provide additional information to the first sentence, it should be considered as new clause which has to begin with new own subject and verb.
3. In addition, my another question is that the same rule could be applied upto the case in which the antecedent of relative is acting as a object for whole sentence as follows;
* “However, this gradual shift requires time, measured not in months or years but in decades or generations.”
Alaways thanking for your usual supporting, and best RGDS,