Hume opens the Enquiry by drawing a distinction between two kinds of philosophical thinking. The first he calls an "easy and obvious philosophy" which serves as a guide for the man of action. Usually written in an elegant and poetic style, this philosophy tries to cultivate our manners by drawing on examples from common life and making us feel the difference between vice and virtue. This philosophy excites the sentiments and leads us to assent to a way of life that we know to be good. Such philosophy--which Hume associates with figures such as Cicero, La Bruyere, and Addison--is generally quite popular and keeps good standing in posterity. It follows from common sense and thus rarely falls into error.
This philosophy is contrasted with the "accurate and abstract philosophy" of the man of reason. Rather than direct our behavior, this philosophy seeks to form our understanding and to uncover the principles that govern our behavior. Rather than rely upon common sense, this philosophy--which Hume associates with figures such as Aristotle, Malebranche, and Locke--proceeds by means of abstract reasoning from the particular to the general. This kind of philosophy has little application once one leaves off philosophical contemplation. Because its reasoning and conclusions often go against common sense, error in this field is not at all uncommon, and as a result it fares rather poorly in posterity and is sometimes rejected altogether.
Common wisdom suggests that this accurate and abstract philosophy is not to be disregarded entirely, but that a good life consists in an appropriate mix of different elements. The philosopher is often looked down upon for being too shut off from the world outside, but those who ignore philosophy entirely are even more despised for their ignorance. We are reasonable beings, and thus aspire to scientific knowledge, but this knowledge is limited. We are also social and active beings, though a purely social life can become tiresome and a life devoted purely to business and action can wear us out. The "easy and obvious" philosophy, then, is often considered an ideal that appropriately combines philosophical reflection with a more active and social life. A life dedicated only to the pursuit of scientific knowledge is usually punished with pensive melancholy, uncertainty, and public disapprobation.
Nonetheless, Hume argues that a careful study of this accurate and abstract philosophy has its virtues. It calls for an exactness and accuracy that can lead to perfection in more practical matters. For instance, the scientific study of anatomy may seem grotesque in itself, but a painter can create beautiful and anatomically precise figures through careful application of its principles. Besides, Hume remarks, on its own, such scientific study is harmless, is good exercise for the mind, and can help bring us to the truth.
The best objection Hume admits against accurate and abstract philosophy is that it is not science, but rather a confused attempt to explain by means of blind prejudice what we do not know. However, Hume notes, this is not a reason to abandon philosophy, but an exhortation to study it more carefully. If we can properly explain the nature and principles that govern human understanding, as Newton has done for the principles that govern planetary orbits, we can reject bad reasoning and proceed more carefully. Though the mental faculties are most present to us, they are very difficult to conceive of precisely and we are still far from uncovering the fundamental principles that we seek. Still, this is only further reason to study them, and while we can often make mistakes through faulty reasoning, this fallibility is hardly just cause to abandon the project altogether.
This first section lays out the framework of Hume's project. He is clearly greatly influenced by the scientific method and empirical philosophy. His stated goal is to do for the mind what Newton has done for matter. Before Newton, we could explain a great deal about planetary orbits and even predict how and where things would move. However, until Newton, we were unable to explain why the planets move as they do. Newton's theory of gravitation gives a clear and simple explanation as to why the planets orbit the sun and why objects on the earth fall toward its center. Hume believes our explanations of human understanding and behavior are in a state similar to that of pre- Newtonian astronomy. We can observe a great deal about how we think and can often reason quite fruitfully, but as yet we have no clear grasp of the principles that underlie our thought and reasoning.