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If Philip is planning a party.
If Philip and planning are identical...then planning would be a predicate nominative. Does Philip = planning... NOT likely. <G>
Is planning is what Philip is doing. Party is what Philip is doing it to. So party is the "object" of the planning...right?
Talking out loud to yourself is very helpful when doing grammar. Ask yourself questions...
To clarify my question before,
I am diagramming sentences. When diagramming, verbs and gerunds go in very different spots. in the sentence Philip is planning a party, it could either be Philip | is \ (gerund goes a stand) planning | party. Or, it could be Philip |is planning| party. Many setences are like this. How can I always tell whether a word ending in ing is in progressive tense if it has a form of "to be" (is planning) or a gerund (is | planning).
2 answers
The word "planning" is not a gerund in this sentence. It's the main verb, with "is" as it's auxiliary (helping) verb.