DEDUCTIVE REASONING. 67 



The above is a syllogism in the mood called Barbara f 

 in the truly barbarous language of ancient logicians ; and 

 the first figure of the syllogism alone contained three other 

 moods which were esteemed distinct forms of argument. 

 But it is worthy of notice that without any real change 

 in our form of inference we readily include these three 

 other moods under it. The negative mood Celarent will 

 be represented by the example 



Neptune is a planet (i) 



No planet has retrograde motion, (2) 



hence Neptune has not retrograde motion. (3) 



If we put A for Neptune, B for planet,and C for * having 

 retrograde motion/ then by the corresponding negative 

 term c, we denote ' riot having retrograde motion.' The 

 premises now fall into the form 



A = AB (i) 



B = Be, (2) 



and by substitution for B, exactly as before, we obtain 



A = ABc. (3) 



What is called in the old logic a particular conclusion 

 may be deduced without any real variation in the sym- 

 bols. Particular quantity is indicated, as before mentioned 

 (p. 49), by joining to the term an indefinite adjective of 

 quantity, such as some, a part, certain, &c., meaning that 

 an unknown part of the term enters into the proposition 

 as subject. Considerable doubt and ambiguity arise out 

 of the question whether the part may not in some cases 

 be the whole, and in the syllogism at least it must be 

 understood in this sense . Now if we take a letter to 

 represent this indefinite part, we need make no change in 



f An explanation of this and other technical terms of the old logic 

 will be found in my 'Elementary Lessons in Logic,' Second Ed. 1871. 

 Macmillan & Co. 



* 'Elementary Lessons in Logic,' pp. 67, 79. 



F 2 



