L 
{continued) 
LEADING OF PROOF — LEADING PRINCIPLE 
Leading of Proof : no concise foreign 
equivalents. The operation bringing up to 
attention, among propositions admitted to be 
true, certain relations between them which 
logically compel the acceptance of a con¬ 
clusion. (C.S.P.) 
Leading Principle: Ger. leitendes Prinzip', 
Fr. principe directeur ; Ital. principio fonda¬ 
mentale. It is of the essence of reasoning that 
the reasoner should proceed, and should be 
conscious of proceeding, according to a general 
habit, or method, which he holds would either 
(according to the kind of reasoning) always 
lead to the truth, provided the premises were 
true ; or, consistently adhered to, would 
eventually approximate indefinitely to the 
truth ; or would be generally conducive to the 
ascertainment of truth, supposing there be 
any ascertainable truth. The effect of this 
habit or method could be stated in a proposi¬ 
tion of which the antecedent should describe 
all possible premises upon which it could 
operate, while the consequent should describe 
how the conclusion to which it would lead 
would be determinately related to those 
premises. Such a proposition is called the 
‘ leading principle’ of the reasoning. 
Two different reasoners might infer the 
same conclusion from the same premises; 
and yet their proceeding might be governed 
by habits which would be formulated in 
different, or even conflicting, leading princi¬ 
ples. Only that man’s reasoning would be 
good whose leading principle was true for all 
possible cases. It is not essential that the 
reasoner should have a distinct apprehension 
of the leading principle of the habit which 
governs his reasoning ; it is sufficient that he 
should be conscious of proceeding according 
II. 
to a general method, and that he should hold 
that that method is generally apt to lead to 
the truth. He may even conceive himself to 
be following one leading principle when, in 
reality, he is following another, and may 
consequently blunder in his conclusion. From 
the effective leading principle, together with 
the premises, the propriety of accepting the 
conclusion in such sense as it is accepted 
follows necessarily in every case. Suppose 
that the leading principle involves two propo¬ 
sitions, L and V’, and suppose that there are 
three premises, P, P', P" ; and let G signify 
the acceptance of the conclusion, as it is 
accepted, either as true, or as a legitimate 
approximation to the truth, or as an assump¬ 
tion conducive to the ascertainment of the 
truth. Then, from the five premises L, V, 
P, P', P", the inference to G would be 
necessary ; but it would not be so from L, L', 
P', P" alone, for, if it were, P would not 
really act as a premise at all. From P' and 
P" as the sole premises, G would follow, if 
the leading principle consisted of L, Land 
P. Or from the four premises L', P, Pf, P", 
the same conclusion would follow if L alone 
were the leading principle. What, then, 
could be the leading principle of the inference 
of G from all five propositions L, L\ P, P\ P", 
taken as premises ? It would be something 
already implied in those premises ; and it 
might be almost any general proposition so 
implied. Leading principles are, therefore, 
of two classes ; and any leading principle 
whose truth is implied in the premises of 
every inference which it governs is called 
a ‘ logical ’ (or, less appropriately, a formal) 
leading principle; while a leading principle 
whose truth is not implied in the premises 
B 
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