Fârâbî takes this result as indicating that dialectic and demonstrative science give different meanings, not only to the “what is X?” question and thus to quiddity (dialectic seeking a nominal definition, science a causal definition), but also to the “whether X is” question and thus to existence. So he says that, as in dialectic the two-place investigation “whether X is Y” is only concerned with the copula (not with whether it is essential predication), so in dialectic the one-place investigatio