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<p>If we suppose ourselves to know no more of man than what is contained in the definition ''Man is the rational animal'', then we might divide man into ''man risible'' and ''man non-risible''.</p>

<p>If we suppose ourselves to know no more of man than what is contained in the definition ''Man is the rational animal'', then we might divide man into ''man risible'' and ''man non-risible''.</p>

<p>Before the information we knew (let us say) that there were certain risible men whom we may denote by ''A'' and there were other men who might or might not be risible whom we will denote by ''BB''’ [&mdash; perhaps ''B'' + ''B''’ was intended?].  We have now found that ''BB''’ are also risible.  When we said all men before we meant ''A'' + ''B'' + ''B''’; when we say all men now we mean the same.  The extension of ''man'' then has not changed.  When we said risible men before we denoted ''A'' + ''B''&nbsp;?, that is to say the whole of ''A'' but none of ''B'' for certain;  but now when we say risible men we denote ''A'' + ''B'' + ''B''’.  Hence the extension of risible men has ''increased'', so as to become equal to that of ''men''.  On the other hand the intension of ''risible man'' is now as it was before, composed of ''risible'', ''rational'', and ''animal''; while the comprehension of ''man'' which before contained only ''rational'' and ''animal'', now contains ''risible'' also.</p>

 

<p>And then the connotation of ''man'' would be less than that of either ''man risible'' or ''man non-risible''.  And conversely ''man risible'' and ''man non-risible'' would have a less extension than ''man''. But we afterwards find that the class ''man non-risible'' does not exist and is impossible.  Henceforward the idea of man and that of risible man are changed.  The ''extension'' of risible man has become equal to that of ''men'' and the comprehension of ''man'' has become equal to that of ''risible man''. And how has this change in the relations of the terms been effected?</p>

<p>Before the information we knew (let us say) that there were certain risible men whom we may denote by ''A'' and there were other men who might or might not be risible whom we will denote by ''BB''’ [— perhaps ''B'' + ''B''’ was intended?].  We have now found that ''BB''’ are also risible.  When we said all men before we meant ''A'' + ''B'' + ''B''’;  when we say all men now we mean the same.  The extension of ''man'' then has not changed.  When we said risible men before we denoted ''A'' + ''B''&nbsp;?, that is to say the whole of ''A'' but none of ''B'' for certain;  but now when we say risible men we denote ''A'' + ''B'' + ''B''’.  Hence the extension of risible men has ''increased'', so as to become equal to that of ''men''.  On the other hand the intension of ''risible man'' is now as it was before, composed of ''risible'', ''rational'', and ''animal'';  while the comprehension of ''man'' which before contained only ''rational'' and ''animal'', now contains ''risible'' also.  (Peirce 1865, "Harvard Lecture 10.  Grounds of Induction", CE 1, 275–276).</p>

<p>(Peirce 1865, Harvard Lecture 10 : Grounds of Induction, CE 1, 275&ndash;276).</p>

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