Leibniz's three simple arguments that the mind must contain innate (a priori) 



Proposition to be proven: The (human) Mind is not a Tabula Rasa [blank slate] 

T1.1 : Because it contains principles on which necessary truths rest, and these 
principles did not originate outside the mind. 

T1.2 : Because it contains ideas of reflection, i.e it is itself the source of 
inner knowledge. 


P1 The Mind knows both truths of matter of fact and truths of reason  

P2 The Mind knows truths of reason (from P1 by Simplification) 

P3 The truths of reason are necessary, universally valid (true in all possible 
words) and absolutely certain 

C1 Therefore the Mind knows necessary and universal truths (from P2 and P3 by 

P4 Necessity, universality and certainty can either be established by means of 
induction from external sensory data or they may originate from the mind 

P5 Induction is inadequate in yielding necessity, universal validity and 

C2 Therefore necessity, universal validity and certainty of truths of reason 
can be original with the mind itself. (from C1, and P4 & P5 with Disjunctive 

P6 If necessity and certainty are original with the mind, then they are 
contained within it. 

C3 Hence the mind contains these originally in itself (from P6, C2 and 

P7 If the mind contains originally an item of knowledge, then the mind is not 
empty ever.  

C4 Therefore the mind is not empty ever. (from C3 and P7 and Modus Ponens) 


P1 The mind has Ideas by means of Reflection 

P2 Ideas of Reflection manifest the capacity of the mind to know itself. 

P3 The mind can know itself inwardly either by relying on the senses for 
assistance or it is itself endowed with this capacity. 

P4 The senses can deliver knowledge (ideas) regarding only the external world. 

C1 Hence the mind's capacity for reflecting on itself is an endowed capacity. 
(from P3 and P4 and Disjunctive Syllogism) 

P5 If the mind possesses an endowed capacity, then it contains it in itself 
without having it acquired. 

C2 The mind contains without acquiring the reflecting capacity (from C1, P5 and 
Modus Ponens) 

P6 If a mental item is contained in the mind without being acquired, then it is 

C3 Hence the mind's reflecting capacity is innate (from C2 and P6 and Modus 

P7 If the mind has an innate item, then it cannot be empty at its inception  

P10 If the mind contains something innately (from its inception) then it 
contains it continuously. 

C4 Therefore the mind is not empty ever (from P7 and P10 and Hypothetical 

T2 Proposition to be proven: that the mind has the capacity of actively 
searching and finding innate truths within itself, not merely knowing them. In 
other words: The capacity to know these truths is different from the capacity 
the understanding has of merely being capable of coming to know (receive) them. 

P1 Either a mental faculty is a bare faculty or it is a predetermined, 
dedicated, capacity to search for specific objects in the mind 

P2 An epistemic faculty is a 'bare faculty' iff it is merely an indeterminate 
disposition to receive truths (by definition) 

C1 Therefore a mental faculty is either an indeterminate disposition to receive 
truths or a redetermined, dedicated, capacity to search for specific truths in 
the mind (from P1 and P2 by Substitution) P3 
The epistemic capacity of knowing necessary truths is a mental faculty 

C2 Therefore the epistemic capacity of knowing necessary truths is either a 
bare faculty or a predetermined dedicated capacity to search for specific such 
truths (from C1 and P3 by Substitution) 

P4 If the epistemic capacity of knowing necessary truths is a bare faculty of 
receiving, then it is not the source of such truths 

P5 T1.1. (above) has shown that the mind is the source of the validity (proof) 
of necessary truths 

C3 Therefore the epistemic capacity of knowing necessary truths is not a bare 
faculty (fromP4 and P5 and Modus Tollens) 

C4 Therefore the epistemic capacity of knowing necessary truths is a 
predetermined dedicated capacity to search for specific objects (from P1 and C3 
with Disjunctive Syllogism) 
 I have also used the analogy of the veined block of marble, as opposed to an 
entirely homogeneous block of marble, or to a blank tablet...[I]f there were 
veins in the block which marked out the shape of Hercules rather than other 
shapes, then the block would be more determined to that shape and  
Hercules would be innate to it...even though labour would be required to expose 
the veins and to polish them to clarity, removing everything that prevents them 
from being seen. This is how ideas and truths are innate in us as inclinations, 
dispositions, tendencies, or natural potentialities and not as action; although 
these potentialities are 
always accompanied by certain actions, often insensible ones, which correspond 
to them.(5) [A]t every moment there is in us an infinity of  perceptions 
unaccompanied by awareness or reflection; that is alterations in the soul 
itself, of which we are unaware because 
these impressions are either too minute and too numerous or elsetoo 
unvarying...But when they are combined with others they do nevertheless have 
their effect and make themselves felt. (6) [A] special affinity which the human 
mind has with [necessary truths]...is what makes us call them innate. So it is 
not a bare faculty...a mere possibility of understanding those truths;
 it is rather a disposition...a preformation which determines our souls and 
brings it about that they are derivable from it. (7) [A] 'consideration of the 
nature of things' is nothing but 
the knowledge of the nature of our mind and of those innate ideas, and there is 
no need to look for them outside oneself .  

(New Essays on Human Understanding, Preface and Bk. Ch.i.) "

Dr. Roger B Clough NIST (ret.) [1/1/2000] 
See my Leibniz site at 

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