This main thesis leads to two lines of argument.First of all,Mill seeks to show that the methods of proof expounded by his adversaries do not really take us beyond experience;and,secondly,he seeks to show that experience gives us a sufficient basis of knowledge.Let us first notice,then,how the ground is cleared by examining previous accounts of the process of inference.The old theory of reasoning depends upon the syllogism.That gives the type of the whole process by which knowledge is extended.All men are mortal;Socrates is a man,therefore Socrates is mortal.Stewart and Brown had both attacked the syllogism on the familiar ground that it is tautologous.The major has already asserted the minor.To say that one man is mortal when you have already said that all men are mortal,is merely to repeat yourself.There can be no real inference,and no advance to new knowledge.So long as the syllogism is to be explained on the old terms,Mill thinks this criticism fatal;but he holds,too,that by a different interpretation we may assign a real and vitally important meaning to this venerable form of argument.In several places(26)he gives a view which seems to be much to the purpose.The syllogism,it would seem,corresponds really,not to a mode of reasoning,but to a system of arguing.
When a disputant bases some statement upon an inference,we may challenge either the truth of the rule or the statement of fact.
The cogency of the argument depends upon the applicability of the rule to the fact.If men be not mortal,or,again,if Socrates be not a man,the inference is not valid;and these two distinct issues,the issue of law and the issue of fact,may be raised in any case.(27)The value of the syllogism is that it raises these issues distinctly.The argument is thus put in such a form as to be absolutely conclusive if the premises be themselves granted.
It therefore provides a test of the validity of the logic.
Granting the premises,a denial of the inference must involve a contradiction.That is the only test in pure logic.The syllogism must,therefore,be in a sense tautologous,for otherwise it could not be conclusive.Acceptance o?the premises must be shown from the form of statement to necessitate the admission of the inference.This follows,and the logical link is complete and irrefragable,if the middle term be identical in both premises,and not otherwise.This is what Mill indicates by saying that 'the rules of the syllogism are rules for compelling a person to be aware of the whole of what he must undertake to defend if he persists in maintaining his conclusion.'(28)Ratiocination,as he sums up his view elsewhere,'does not consist of syllogisms';but the syllogism is a useful formula into which it can 'translate its reasonings,'and so guarantee their correctness.(29)If this be granted,we must consider the essential step of inference to be embodied in,but not created by,the syllogism.Correct reasoning can always be thrown into this form.The syllogism emerges when the reasoning is complete.
'The use of the syllogism is no other,'says Mill,'than the use of general propositions in reasoning.'It is a security for correct generalisation.(30)We have,then,still to ask what is the reasoning process for which the syllogism provides a test.
Generalisation implies classification.Our general rule or major premise states some property of a class to which the individual belongs.The question is how this reference to a class enables us to draw inferences which we could not draw from the individual case.To this Mill gives a simple answer,which is already implied in his theory of predication.When I say that Socrates is a man,I say that he has the attributes connoted by the name.He is a rational,featherless biped,for example.But I already know by observation that with these attributes goes the attribute of mortality.The essence of the reasoning process is therefore that,from the possession of certain attributes,I infer the possession of another attribute which has coexisted with them previously.That I do,in fact,reason in this way in countless cases is undeniable.I know that a certain quality,say malleability,goes along with other qualities of colour,shape,and so forth,by which I recognise a substance as gold.I can,it may be,give no other reason for believing the future conjunction of those qualities than the fact of their previous conjunction.
The belief,that is,is as a matter of fact generated simply by the previous coincidence or corresponds to constant association.
Whether this exhausts the whole logical significance may still be disputed;but,at any rate,upon these terms we can escape from the charge of tautology.The rule in the major premise registers a number of previous experiences of coexistence.When we notice some of the attributes in a given case,we make an addition to our knowledge by applying the rule,that is,by inferring that another attribute may be added to the observed attributes.This,then,gives a rational account of the advance in knowledge made through the syllogism in the case where the class can be defined as a simple sum of attributes.
But is this an adequate account of the reasoning process in general?There is another view which suggested difficulties to Mill.His solution of these difficulties,marked,as we learn from the Autobiography,an essential stage in the development of his doctrine.Reference to a class is,upon his interpretation,implied in the syllogism;and classification implies definition.
