extension whether extension includes whole domain ref name magnus ref quantification allowed individual terms predicates contrast higher order logics ref name v n nen ref ref name hintikka extended logics alethic modal alethic modal logic influential logic philosophy provides logical formalism express ''possibly'' ''necessarily true'' ref name cambridge ref name britannica ref name garson ref ref name benthem ref ref name burgess ref ref name macmillannonclassical constitutes extension first order logic able express ''true simpliciter'' extension happens introducing two new symbols possibility
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