But Dr.Keynes defends it on the ground that (1) it is obtained by obversions and conversions which are all legitimate and (2) that although _All A is B_ does not distribute _B_ in relation to _A_, it does distribute _B_ in relation to some _not-A_ (namely, in relation to whatever _not-A_ is _not-B_).

This is one reason why, in stating the rule in chap.vi.Sec.6, I have written: "an immediate inference ought to contain nothing that is not contained, _or formally implied_, in the proposition from which it is inferred"; and have maintained that every term formally implies its contradictory within the _suppositio_.
Sec.11.Immediate Inferences from Conditionals are those which consist--( 1) in changing a Disjunctive into a Hypothetical, or a Hypothetical into a Disjunctive, or either into a Categorical; and (2) in the relations of Opposition and the equivalences of Obversion, Conversion, and secondary or compound processes, which we have already examined in respect of Categoricals.

As no new principles are involved, it may suffice to exhibit some of the results.
We have already seen (chap.v.Sec.

4) how Disjunctives may be read as Hypotheticals and Hypotheticals as Categoricals.

And, as to Opposition, if we recognise four forms of Hypothetical A.I.