Are we not often at times shocked by the discovery that what we thought was certain is later proved dubious and false? If this be a regular occurrence, is it not the case that we may become suspicious of all claims to certainty? But then, the history of human opinion rightly forms the most fertile source material for the development of any theory of knowledge. Yet, no theory or belief has proved so full of absurdity, that it lacked its own disciples. The history of science is itself replete with theories priory accepted by the sages of old but later on discredited.
Philosophers are therefore concerned with the basis of all knowledge claims, so that they might arrive at a consensus for judging these claims. For it, much of what had been taken as certain has instead been proved false or sceptical. Then, what can we really know and how can we really ever be certain?
Such were the feelings of David Hume, as he posited his philosophy of “impression and ideas” of which this work is to throw more light on.
The philosophy of David Hume then is both an attack on rationalism and a “reducto and absurdum” of empiricism since the empiricism he defines is one-sided as the rationalism he attacks. He frankly confessed his dissatisfaction with his position in a passage which seems to be the starting point for a consideration of the outline of his work.:
There are two principles which I cannot render consistent nor is it in my power to renounce either of them, namely, that all our distinct perceptions are distinct existence, and that the mind never perceives any real connection among distinct existence.
Thus, the appeal to those two principles and the understanding of them is the key of Hume’s work. The first principle, that what we can distinguish in perception is distinguished in existence is subjective. I rather see it as making the articulations and distinctions of things depend on the distinctions of the mind. But the second principle is based on the opposite assumptions.
Hume’s whole account of causation depends on his perception that causation is not a relation among the mind’s own ideas, in the sense that it can be got at by any kind of introspection or reflection. Thus, the result of Hume’s theory of causation seems to be subjective when he reduces the conception of necessary connection to a feeling, and this is precisely because he believes that causation is a relation between real existences and cannot be perceived by the mind. About causation, he said:
Causation is a relation, which can be traced beyond our senses and informs us of existence and objects, which we do not see or feel.
In Hume’s philosophy, the theory of the “association of ideas” plays the most important part and was the most recognized in the later history of English Empiricism. No wonder Hume was constantly making association the work of the understanding and through this theory, he succeeded in narrowing the fundamental principles of knowledge to mere feeling. His account of the general principle; also lobbied his explanation of particular instances of cause and effect. Thus, little did he mean to think that by causation, we only mean constant conjunction, but that we sometimes infer causation from the observation of only one instance.
In his own period, Hume affected the inheritance of the Cartesian rationalism into empiricism and made atomization of perception the very nerve of his philosophy. From this insight, he viewed every question especially metaphysical and proposed every solution.
It is then our task in this work, to expose the implications of the concept of his “impressions – ideas” theory, which evidently forms his basic epistemological stand. We shall therefore see how plausible they are with a critical mind.
1.1 Statement of the Problem
The genesis of the history of philosophy is the treatment of the Ionian philosophers whose main concern was to determine the basic constitution of the material substances of the universe.
In this immortal search, Thales posited water, Anaximander posited air, and Pythagoras came up with units i.e. the mathematical numbers. The departure of Pythagoras and his subsequent followers was a gathering storm, which ushered in a sharp digression in philosophical inquiry. Attention now shifted to the problem of change and permanence. In this pre-Socratic era philosophy was more cosmocentric in nature.
Plato in the ancient period posited the world of forms, saying that the real things exist in the worlds of ideas. Socrates also on his part believes that knowledge is certain, objective and universal. It is quite possible for man to acquire knowledge. His was the dialectical method i.e. beginning from particular cases and concluding with universal knowledge.
In the Mediaeval period, Augustine toes the line of Plato. Augustine distrusted the senses as source of knowledge. The senses in his view do not give us certain knowledge. The objects of knowledge are not the material things of this world, but the external ideas in the mind of God. St Thomas is said by some scholars to have succeeded merely in Christianizing Aristotle. These mediaeval or Christian philosophers were influenced by the church supremacy at their time.
In this period, the movement was actually a rebirth of knowledge, a revival of interest and zeal for knowledge. It began with a renewed interest in Ancient writings and eventually developed into humanistic and scientific movements, with emphasis on man rather than God. Two important schools flourished in this period.
The continental rationalists (Descartes Spinoza and Leibniz) adopted the mathematical method and believed that reason alone, using the mathematical method can attain truth without the aid of the senses. They denied that sense perception was necessary in order to attain knowledge. The empiricists on the other hand, asserted that all-genuine knowledge derive from sense perception. Neither Locke nor Berkeley was a consistent empiricist. But Hume was and he brought empiricism to its logical conclusion. He tried to portray this by his philosophy of impression and idea. When we perceive objects, they make impression on us. Ideas are formed from these impressions. Whether he succeeded in doing this is what we shall be looking at in this work. We shall be evaluating critically his position about impression and idea, within which we shall portray the explicit implication of his position.
My aim or purpose in this research now is to expose the implications of the concept of Hume’s impressions and ideas theory. We shall therefore see how plausible they are, with a critical mind. This work will seek to x-ray the extent to which pure knowledge can be gotten only through impression or that we can only know something through experience and without impression, there will be no ideas.
This research does not intend to give an exhaustive study of David Hume’s philosophies. Rather, it centered on his theory of impression and idea. How he tried to resolve the diverse conceptions of philosophers on the acquisition of pure knowledge.
1.4 The Methodology of the Work
In this sensitive philosophical discourse, we shall make use of expository method in understanding the notion of impression and ideas and Hume’s argument in denying and rejecting reason as a way of attaining knowledge. Again, we shall use critical method in evaluating Hume’s view. In general, the methodology is going to be scholarly, academic, and philosophical.
This research work is divided into five chapters. Chapter one deals mainly with the introduction and the framework of the entire study, chapter two deals with the literature review. This takes into account the contributions of other philosophers on the related topic in the various epochs. Chapter three x-rays the Epistemological foundation of Hume’s philosophy, chapter four centered on the impossibility of the metaphysics while chapter five gives an evaluation and critical conclusion to the work.
 D. Hume, A Treatise of Human Nature ed, L. A. Selby, Bigge, (London: Ely House, Oxford University Press, 1975), p. 636.
 Ibid, Bk 1, Part III, Section II, p.179
 E. Anowai, Unpublished Lecture on Cosmology,(Awka: P.J.P.S ,2004), p.24
 Ibid. p. 25
 J. Omoregbe; Epistemology – A Systematic And Historical Study, (Lagos, Joja Educational Research, 2003), p. 89.