Pierre Gassendi was a French philosopher, astronomer, empiricist, and priest who lived from 1592-1655. Gassendi believed that knowledge and evidence of the external world derived from sensory experience, and that every sense experience is subjective to an individual. In determining his own philosophy, Gassendi constantly reviewed other sources and offered a wide range of views – in agreement or in contrast of his own – to help frame questions he had or answers to these questions. He often used ancient theories of knowledge to help understand current philosophical dilemmas. Philosophically, Gassendi is most well known for his rejections of Cartesian and Aristotalian views, and for the promotion and introduction of Epicurean views into mainstream European thought. Gassendi was also a very active astronomer – there is even a crater on the moon named after him.
One of Gassendi’s most notable arguments were his disputes with Descartes on his work Meditations (1641). Descartes asserts that as beings we can only perceive appearances, and these appearances are not subjective to each individual. In opposition to that theory, Gassendi proposes that each experience varies subjectively, and because of that we cannot determine a common appearance or essence of an object if we all perceive it differently. Gassendi also refutes Descartes’ argument in regards to the mind and body. Descartes believes that the mind and body have completely different natures, and therefore cannot be the same. He additionally states that the mind may have an effect on the body even though they are not necessarily connected. Gassendi objected to this argument and questioned how the mind and body could have any type of interaction if they were not connected and the mind could not be extended.
Gassendi heavily disputed Aristotalian views as well. Primarily, Gassendi believes that there is nothing necessary about the world and how it acts; this belief is directly opposite of Aristotle’s on this subject. Gassendi also proposes that we have no way of knowing fundamental properties of a substance and if they are subject to change or not; we can only develop knowledge through our sensory experience.
Though Gassendi seemed to refute a lot of former philosophers that he studied, he promoted certain ones too. He was most commonly known to advocate for ideas from Epicurus, and wanted to revive Epicureanism. Gassendi promoted Epicurean ideas regarding the conception of knowledge. Further, Gassendi deeply believed in atomism, which was one of Epicurus core beliefs. Gassendi agreed with the concept that atoms were eternal, varied in size and shape, and moved at different speeds. He asserted that atoms were extended and that when atoms interact with each other they cause things to happen, which we then see as events in the world. But, Epicurus argued for the infinity of the number of atoms in our universe, while Gassendi did not. Gassendi asserted that the number of atoms within our universe wass very, very large, but still finite.
Another big part of Gassendi’s life and work was scientific studies, specifically astronomy. Gassendi believes that time and space are absolute and infinite. He states that space and time are both categories of existence. He theorized that the flow of time never stops, that space is extended regardless of any factors, and that both of them pre-date creation. This theory of Gassendi’s directly opposes Descartes’ thoughts on the subject.
Moreover, Gassendi was a strong empiricist and user of the scientific method, constantly emphasizing the importance of sensory experience as evidence of knowledge as supposed to theories or innate beliefs. He tells us that we can and should trust our senses and trust that the knowledge we develop from our experience is subjectively true. Gassendi’s variety of experience, thorough counterarguments to Descartes and Aristotle and relentless belief in the scientific and empirical methods continued to influence many famous philosophers after him such as Boyle, Locke, and Newton. His philosophy helped advance our understanding of empiricism and established new ideas into common European thought.