Complex sentence: In philosophy possible worlds are usually regarded as real but abstract possibilities, but at times as a mere metaphor, abbreviation or "façon de parler" for sets of counterfactual propositions.
Split into simpler sentences: In philosophy possible worlds are usually regarded as real but abstract possibilities. Some other times, as non-real, as a mere metaphor, abbreviation or "façon de parler" for sets of counterfactual propositions.