Mode of Reasoning-Locke and Descartes

Descartes: Before we got interrupted, you were telling me something about mental perceptions…

Locke: Yes, mental perceptions or contents exist in two forms and these are ideas and impressions. Current experiences like feelings, sensations, emotions and desires to name but a few are what can be considered impressions (Carruthers, 2005). On the other hand, we derive ideas from our impressions. Ideas can be simple or complex. Simple ideas can be classified into primary and secondary qualities with primary qualities being those that the object possesses independent of us for example motion, texture and solidity and secondary qualities being those that are produced by primary qualities of the body itself and their perception which depends on the normal operation of the senses for example color, taste and sound among others (Kenny, 2001). Complex ideas are a combination of simple ideas derived by transposing, compounding, diminishing or augmenting impressions (Aune, 2004).

Descartes: Where are these ideas obtained from?

Locke: Ideas are obtained from two sources, sensation and reflection. Through sensation, ideas are produced immediately after an exposure to an experience through the sensory organs (Carruthers, 2005). Human senses are already conversant with certain sensible objects and these, the senses convey to the mind in a number of distinct perceptions, for example color, sound, smells etcetera (Aune, 2004). The second source of ideas is reflection which is the way through which the mind can understand and produce ideas by perception. Human beings reflect within their own minds upon the ideas they obtain through sensation. This furnishes them with a new set of ideas that cannot be obtained from anywhere else (Carruthers, 2005).  

Descartes: So what is knowledge to you?

Locke: A human being starts to have ideas when he experiences his first sensation (Kenny, 2001). The mind as mentioned earlier is a blank slate without any prior innate ideas and as such it is until an impression is made in some part of the body that a human being will first develop a perception of an idea (Aune, 2004). I need to also add that the first capacity of human intellect is that be it through sensation or reflection, the human mind is developed in such a way that it can receive impressions. This is the first step for human beings to discover anything in this world and thus through the two processes of sensation and reflection, they gather ideas that eventually become knowledge (Kenny, 2001). My understanding of knowledge therefore is that it is the result of a perception of ideas which may be in accordance or discordance with each other and which is only gained through experience (Carruthers, 2005).

Descartes: Only gained through experience? The human mind at birth already has innate ideas and knowledge?!

Locke: That is where you are going wrong. The human mind at birth is a blank slate containing no prior innate knowledge. From the time a child is born, various alterations take place. Its mind through the senses become furnished more and more with ideas and this causes the mind to become more awake and to think more (Kenny, 2001). As time goes by, the child will start to know certain objects that he is familiar with the most and which have had lasting impressions on him. Starting to know things is a process for the child and as he continues conversing himself with them, he is able to distinguish between what is familiar and what is strange (Aune, 2004). The ultimate beginning of all human knowledge therefore is sense experience. It is the senses that provide us with all the raw data we require to understand the world and therefore without the senses there is no knowledge. It is after we perceive through our senses that we create a belief system that ultimately becomes our knowledge.

Descartes: That is not true. The ultimate beginning of all human knowledge is reason and not the senses as you claim. There exist certain ideas which I call ‘priori’ that through biology are carried in the mind (Kenny, 2001). When an infant is born, these priori ideas have already been acquired through reason.

Locke: I am listening, go on.

Descartes: Now, this is the point, without these prior principles and categories, we do not have the capacity to organize or even interpret the experience we gain from our senses. Without these priori ideas, human beings would be faced by one undifferentiated, huge and kaleidoscopic whirl of sensations that have no significance (Carruthers, 2005). When the mind of an infant begins working, it does so in two hundred and fifty six different ways. This of course does not include induction which is the method through which we identify our perceptions. The infant will soon seek which one of the two hundred and fifty six methods actually work and the truth is that only fifteen of them work (Aune, 2004). The other two hundred and forty one methods cannot be said to work because they only lead to false conclusions. The infant therefore will result to throwing the fallacies out once he realizes that they do not work (Kenny, 2001). Reason therefore is the ultimate beginning of all human knowledge since it is through it that innate knowledge is generated and certified (Carruthers, 2005).  If I may ask, supposing the human mind is a blank slate at birth as you claim, without any ideas or characters, how then it is furnished? Where do all these varying materials of knowledge and reason then come from?

Locke: It is from experience. All our knowledge is founded from experience and this is how it happens. We employ observations either about our mind’s internal operations or about external sensible objects which we then perceive and reflect on. Doing so supplies us with the understanding of all thinking materials (Carruthers, 2005).  

Descartes: Have you considered how correct the knowledge obtained from experience is? For example, when you observe the sun through our senses, it appears smaller in size but in reality it is not!

Locke: It is until we become aware of the representations of external objects that we can be aware of the external objects themselves. For example, an object cannot be described as “red” in color if prior knowledge of what “red” should look like is unknown (Carruthers, 2005). As such, the “red color” idea is in our minds and not with the external object.

Descartes: What you have said is true. We cannot rely fully on our senses in order to gain knowledge. Things can only be fully and correctly known through both our senses and reason.


Aune, B. (2004). Rationalism, Empiricism and Pragmatism: An Introduction. New York: Random House.

Carruthers, P. (2005). Human Knowledge and Human Nature. Oxford: Oxford University Press.

Kenny, A. (2001). Rationalism, Empiricism and Idealism. Oxford: Oxford University Press



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