In the eighteenth century, there were two major schools of thought in the field of moral philosophy: rationalism and empiricism.
The rationalist school of thought argues that all knowledge and truth is innate in human beings and could be discovered through deductive reasoning. In that view, logical thinking is the pathway to truth. The empiricist school of thought suggests that all knowledge and truth is derived from experience. Proponents favor inductive reasoning, claiming that it is observation and reflection that leads to truth. In their view, sensory perceptions, not innate ideas, enable human beings to discover the truth.
David Hume adopts the empirical school of thought. To him, ideas are not ascertainable by pure reason alone. He rejects the rationale that ideas are implanted in the minds of humans at birth. In his view, the world has no rational foundation. Instead, human beings learn about the world through psychological associations based on sensory perceptions. Therefore, to reach moral judgments, humans must experience life through their senses. Hume denies that the human mind comes pre-infused with knowledge requiring only reason to arrive at the truth. He believes that reason is a function of knowledge, not a source of it. Where rationalists believe that knowledge is innate to human beings and thinking hard about things in nature results in learning about reality, empiricists argue that the principal source of knowledge is sensory perceptions or feelings. A weakness of this thinking lies in the fact that moral judgments are sometimes made on impulse.
Hume accepts John Locke’s concept of tabula rasa, from the Latin meaning “blank slate.” He believes that when humans are born, they have no knowledge. Prior to making moral judgments, they must experience life through the senses. Hume posits that the brain is not simply a depository of thoughts, but rather an organ used to organize and analyze the knowledge acquired empirically. Once analyzed through an evaluation of sensory perceptions, moral judgments can be made.
Immanuel Kant is one of the most influential philosophers of the Enlightenment period. Kant attempts to mold the two traditional approaches of rationalism and empiricism into a single ideology. He attempts to develop a merger of ideas dividing the prevailing ideologies.
Kant favors the development of a pure moral philosophy by virtue of what he calls “transcendental idealism.” He argues a distinction between the observable world and the metaphysical world that is impossible to observe. In the development of a moral philosophy, he allows for the discovery of meaning in a material world through an empirical approach, but he insists on the necessity of free will and rationality to provide life with purpose. He concludes that humans must make sense of their experiences. Objects they perceive to be accurate in the world outside their thoughts might not be so in reality. To Kant, making sense of human actions and experiences must include a universal moral duty applicable to all. Although he believes human beings have the freedom to act, he warns that life is only meaningful if people adhere to a uniform code of duty. This pure moral philosophy conceptualized in what he refers to as the “Categorical Imperative” is the view that people must treat others consistently, acknowledging the self-worth of all human beings.