  Aristotle restricts and regiments the types of categorical sentence that may feature in a syllogism. The admissible truth-bearers are now defined as each containing two different terms (horoi) conjoined by the copula, of which one (the predicate term) is said of the other (the subject term) either affirmatively or negatively. Aristotle never comes clear on the question whether terms are things (e.g., non-empty classes) or linguistic expressions for these things. Only universal and particular sentences are discussed. Singular sentences seem to be excluded and indefinite sentences are mostly ignored. At An. Pr. A 7 Aristotle mentions that by substituting an indefinite premise for a particular, one obtains a syllogism of the same kind.