For the term 'bats,' being excluded from the whole of the term 'lay eggs,' is thereby necessarily excluded from that part of it which coincides with 'birds.'
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CHAPTER XI.
Of the Generad Rules of Syllogism.
§ 582. We now proceed to lay down certain general rules to which all valid syllogisms must conform. These are divided into primary and derivative.
I. Primary.
(1) A syllogism must consist of three propositions only.
(2) A syllogism must consist of three terms only.
(3) The middle term must be distributed at least once in the premisses.
(4) No term must be distributed in the conclusion which was not distributed in the premisses.