Enlightenment Roots: Pierre Gassendi

The doctrine of the Stoics or of any other sect as to the force of Destiny is a bubble engendered by the imagination of man, and is near akin to Atheism. I not only believe in one God, but my faith as a Christian is also grafted upon that tree of philosophy which has never spoiled anything.
(Casanova’s Memoirs – Author’s Preface)

Pierre Gassendi (1592 to 1655) was an early Enlightenment scholar, if lesser known today than such giants as Bacon, Descartes, Hobbes, Newton, Locke and Spinoza.  He was, nonetheless, an influential figure who connects the philosophers of ancient Greece with the scientists of today and thus illuminates the transitioning of the medieval world into the modern.  He is also particularly important for anyone interested in tracing and evaluating Casanova’s own philosophy and ideas, introduced to Gassendi’s writings as he was when he was in his very formative teen years.  Gassendi was born in Champtercier in the south of France, the son of a peasant farmer, and studied philosophy at the University of Aix-en-Provence.  In 1614, he obtained a doctorate in Theology and, in 1617, was ordained a priest, eventually rising to become provost of the Cathedral Chapter of Digne.  In 1617, he was also awarded the chair of Philosophy at the University Aix-en-Provence where he lectured on Aristotle.  However, disquiet over his criticisms of Aristotelianism and the assuming of control of the university by the Jesuits subsequently forced him out of that position.  Gassendi had something of an itinerant lifestyle, travelling around Provence and regularly visiting Paris.

A key facilitator of European intellectual debate at this time was friar, mathematician and polymath Marin Mersenne, (1588 to 1648) dubbed ‘the secretary of learned Europe’, who engaged and corresponded with the foremost scholars of the day, including Descartes (1596 to 1650) who was also a friend.  Mersenne made introductions, communicated information, raised theoretical queries, translated texts and supplied and published books (including one of Hobbes’ optical treatises).  It was largely Mersenne who introduced Galileo to France.  In Paris, from 1633, he was at the centre of regular meetings of mathematicians and physicists, in many ways a precursor of the Royal Society (1660) and the Académie des sciences (1666).   Mersenne’s informal network highlights how new radical theories and ideas were able to side-step the constraints of formal educational institutions such as universities that were controlled by the Church and dominated by the centuries-old orthodoxies of Aristotelian scholasticism (see ‘Enlightenment Roots: Introduction‘).

The activities of Mersenne and the scholars with whom he communicated were a symptom of the crisis of authority that had been convulsing Europe since the Reformation.  The establishment of competing faiths undermined the once unquestioned textual authority of the scriptures, Church Fathers and ancient classical philosophers upon which the edifice of Medieval Christian thought rested.  The work of natural philosophers such as Copernicus and Galileo, who demolished the idea that the Earth was at the centre of the universe, undermined this authority even further.  Men such as Mersenne, Gassendi and Descartes were in the vanguard of those trying to work through the implications of this epistemological challenge: how was knowledge possible in the absence of textual authority?  One answer, to be found in the works of ancient skeptics such as Pyrrho and Timon, was that it wasn’t.  Descartes’ response, on the other hand, was to attempt to build the foundations of knowledge on the certainty of the existence of the individual self (‘I think therefore I am’).  This epistemological individualism, while discarding the Aristotelian explanation of natural phenomena, accepted Aristotle’s premise that scientific knowledge had to be certain.  To this certainty Descartes added his ontological proof of the existence of God and built up from there.

Through one of Gassendi’s patrons, Claude Fabbri de Pereisc, Mersenne met Gassendi and the two became close friends, Mersenne encouraging his work and introducing him to Descartes along with others.  In 1642, in what was to become a very public dispute, Gassendi published his objections to Descartes’ propositions in which he attacked his failure to establish the reality of innate ideas (as a defence against solipsism, Descartes had asserted that clear and distinct innate ideas must be true). He also highlighted, in particular, the mind-body problem.  Descartes maintained that the body and the mind were distinct entities: the body was material, non-thinking and extended through space; the mind was immaterial, thinking and non-extended (ie, the soul).  If that was the case, however, Gassendi queried, how could the two interact?  By what mechanism could the mind direct the body?  Descartes posited, in response, the idea of a mind-body union which, he asserted, made the question of interaction redundant.  A similar causal problem afflicted the Aristotelian-scholastic tradition.  By what mechanism could a Platonic form or essence interact with or fashion material substance?

Gassendi’s own approach to the epistemological problem of the foundation of knowledge rejected both the fatalism of the ancient skeptics and the requirement for certainty demanded by Aristotle and Descartes.  For Gassendi, scientific knowledge (i.e. knowledge of natural phenomena) could only be probabilistic, dependent upon the strength of the material evidence and argument that supported it.  The stronger the evidence, the more probable the truth claim.  The empirical nature of such knowledge, however, always allowed the possibility of contradictory evidence being discovered at some future point.  It is very likely that Gassendi’s ideas influenced the thinking of Locke and certainly today it is Gassendi’s probabilistic conception of knowledge which dominates scientific thought.   Arguably, this is also the conception of knowledge that is most typical of the Western mindset generally.

Gassendi developed an early interest in mechanical philosophy and the work of Epicurus (341BC to 270BC) and his followers as a consequence of contact in 1629 with a learned Dutch schoolmaster called Isaac Beeckman (1588 to 1637).  Supporters of mechanical philosophy believed in action by contact and rejected the idea of attractive forces and action at a distance.  Gassendi’s engagement with Epicurean ideas was to profoundly influence his own thought.  Epicurus explored the idea of a good life and concluded that it was one that maximised pleasure and minimised pain.  As well as bodily pain he identified fear of gods and punishment in the afterlife as significant causes of distress.  To combat these sources of anxiety he sought to rule out divine intervention and to explain all phenomena in the natural and human world in mechanical and materialistic terms.  Key aspects of Epicurean philosophy included a belief that the aim of philosophy was to attain tranquillity, that man possessed freewill, that our soul did not continue after death, that the natural world was based upon the interaction of atoms in a void and, most significantly, that nothing should be believed without empirical evidence and logical deduction.  This latter principal contrasted strongly with the practice of Aristotelian scholasticism whose truth claims about the world were based upon abstract theorising.  What was important for medieval scholars was the internal consistency of their ideas.  Aristotle, Plato, the scriptures, St Augustine and the rest had provided them with a conceptual framework that explained reality (both philosophically and theologically).  Their job was to demonstrate how natural phenomena fitted into that framework.  Evidence from the natural world could not test, in the sense of validate or invalidate, that framework, it could only illustrate it.

Epicurean philosophy was central in enabling Gassendi to construct alternative solutions to the intellectual challenges bedevilling a world founded upon Aristotelian scholasticism.  However, although the rehabilitation of Epicurus was one of the major projects of his life he could not himself be described as an Epicurean.  He accepted some ideas but modified and rejected others.  For example, Gassendi largely accepted Epicurean hedonism in equating pleasure as a good and, vice-versa, the idea that what is good should be judged in terms of the pleasure it generates.  However, unlike Epicurus, he believed that a truly pleasurable life could only be achieved by God.  The best that man could achieve would be a relatively good life. Despite his criticisms of scholasticism Gassendi never wavered in his loyalty to the Catholic Church or in his belief in the correctness of its theology.  Where Christian theology and Epicurean philosophy clashed, Gassendi chose the side of Christian theology.

Borrowing from the Epicurean proposition that the universe was composed of atoms and void, Gassendi provided a coherent account of how macro-level physical structures and behaviour could be related to the inherent properties of atoms at a micro-level, allowing him to ditch, for example, the Platonic idea that the motions of animate creatures had an internal cause (i.e. the soul).  Existence based on atomism appealed to Gassendi as it allowed God more flexibility to intervene in creation than did the immutable essences of things as posited by Aristotelian thought.  Moreover, it meant that Christian belief in a creator could be compatible with understanding nature in terms of its component elements.  Gassendi rejected, however, the Epicurean claim that the number and types of atoms were infinite and that atoms and the void were eternal as this would imply that God did not have the power to create, destroy and preserve as he so wished.  Likewise, he rejected the Epicurean idea that nature exists in the forms it does by a random mechanical process of atoms compounding together.  Instead he supported orthodox Christian theology that all creation was a consequence of divine will and adopted the Aristotelian teleological, or final goals, view (i.e. that nature behaves the way it does because it has a purpose which is intrinsic to its being).  He also diverged from Epicurean thought in other ways: Gassendi believed that true happiness required divine providence and that ‘God directs the world with a special concern for human advantage’; for Epicurus the soul was mortal while for Gassendi it was immortal.

The empirical stance that Gassendi adopts in his criticism of Descartes and the Aristotelians rests upon the relationship between sense perception and knowledge.  The only access we have to the natural world is through our senses.  All our knowledge about nature, therefore, is ultimately derived from the information they provide.  As we cannot perceive essences, universals or immaterial, non-extended entities we cannot claim to have knowledge of them.  They may or may not exist, we simply can’t know.  And even the knowledge we can possess will be uncertain to a greater or lesser degree, given the subjective variation of sense experience.  Reason, for Gassendi, is no better as it’s judgements of reality will be undermined by flawed and partial information.  In fact, knowledge derived from reason would be even less reliable as the problem of faulty or incomplete information would be compounded by the fact that reason itself is liable to make mistakes.  He does allow, however, for the possibility of knowledge of entities only indirectly experienced through the effect they have on entities that we can experience.  Nonetheless, whatever knowledge we possess about the natural world will still only ever be probable and open to contradiction.  Scientific experimentation and observation, however, would allow us to make judgements as to how probable or improbable were any particular claims to knowledge. This was not the same as theologically derived knowledge which he believed did allow the possibility of certainty.

Examples of his hands-on interest in empirical science can be found in his work in astronomy, optics and mechanics with all the practicalities of instrumentation and measurements that entailed.  He made extensive astronomical observations to be able to calculate planetary positions, suggesting that his sympathies lay with heliocentrism (in 1633, due to his advocacy of heliocentrism, Galileo had been found ‘vehemently suspect of heresy’ by the inquisition and kept under house arrest until his death in 1642).  He explored the problem of trying to work out longitude by reference to lunar eclipses.  He used a camera obscura to attempt to calculate the diameter of the moon.  In 1631, confirming a prediction made by Johannes Kepler, he became the first astronomer to witness Mercury’s transit in front of the Sun, which he did in Paris by projecting an image of the Sun from his telescope onto a white screen.  Gassendi was, by contrast, a fierce critic of astrology, the truth claims of which could not be empirically substantiated.  He speculated on the attributes of vision and light, the elasticity of air and considered the nature of forces acting upon a falling body.  In one experiment he confirmed the conclusions of a Galileo thought experiment by dropping a stone from a moving ship, demonstrating that the stone conserved its horizontal speed.  He undertook the earliest attempt to work out the speed of sound by measuring the difference between seeing the flash of a gun and hearing its shot.  He calculated it to be 478.4 metres per second (the actual speed is 331.29 metres).

A very good example of the exchange and propagation of ideas that was taking place in the seventeenth century beyond formal academic institutions can be observed in the relationship between Gassendi and Thomas Hobbes.  Hobbes’ account of nature rooted in mechanical motion was substantially influenced by his contact with Gassendi and the Mersenne circle in the mid-1630s.  It was during this time when Hobbes was visiting Paris that Gassendi was developing his model of a universe based upon inertial and continuous mobility of atoms in a void universe (in 1642, the year of Galileo’s death and the year before the birth of Sir Isaac Newton, he was to be the first thinker to publish the correct formulation of the principle of inertia, this principal being that objects will continue in a straight line at a constant velocity unless acted upon by another force).  For Gassendi, the movement of atoms was due to a faculty or force that existed within the atom itself.   Matter was, therefore, not passive but possessed of an intrinsic compulsion to move.  This atomic motion, he argued, was an attribute of divine will, its precise nature being dependent upon God’s purpose.   Hobbes was to argue that both the natural world and the people in it are determined in every respect by such action of matter in motion.  A person’s behaviour will vary as a response to the external and internal motions of objects acting upon sense perceptions in the same way as the direction of any object of matter will vary in response to the action of another force.  The instinct for self-preservation, experiences of pleasure and pain and the operation of reason will dictate the behaviour of the subject.  There is no soul to play any part in this equation.  This thoroughgoing determinism inevitably denied the possibility of free will in its absolute, incompatibilist, sense.  The ethical implications for Hobbes was that a necessary cause was a sufficient cause.  What an individual desires is what they perceive to be good and what they have an aversion to is what they perceive to be bad.  This self-interest generates a subjective, relativist morality as opposed to an absolutist account of what is good and bad as is typical of a religion such as Christianity.  For Hobbes, individuals left to their own devices would be driven to engage in a ‘war of all against all’ that could only be avoided by means of a social contract in which men and women relinquish to a supreme authority (a sovereign) their freedom to act.

As Gassendi’s thought was influential in shaping the ideas of Hobbes so Hobbes account of the operation of pain and pleasure influenced Gassendi.  For Hobbes, similar to inertial motion, a person will aim to continue in a pleasurable state and avoid death, the cessation of movement.  Both the behaviour of atoms and the behaviour of people are purely mechanical processes.  Gassendi, however, takes Hobbes’ concept of pleasure as a phenomenon which shapes human actions, and integrates them with Christian metaphysics.  In Gassendi’s philosophy pleasure becomes an instrument of providential guidance.  As God instils atoms with perpetual motion, so He instils people with a desire for pleasure.  Gassendi also gives reason a more dynamic role in decision making than Hobbes’ pleasure and pain arithmetic, adopting the free will position of Epicurus.  To do so, however, he has to address the dilemma of determinism.  If God uses pleasure to guide man to the good and all actions in nature are based upon atomic mechanical processes then where is there any space for free will (one of the central Christian defences against the charge that if God created all things then He must also have created evil)?  Gassendi resolves the problem by drawing on his contention that knowledge of the natural world can only ever be probabilistic (which was also his major challenge to the philosophies of Descartes and Aristotelianism).  Sense perception, the ultimate foundation of our knowledge of the natural world, would always be subjective and imperfect.  Movement toward the good, therefore, could not be mechanically determined but required the corrective action of reason (itself very fallible).

Gassendi’s reputation­ and the importance of his legacy in philosophy and science is being somewhat rehabilitated having been overshadowed by Descartes.  He was well known amongst British thinkers and his influence upon major figures such as Hobbes, Boyle, Locke, Newton and Hume are being increasingly recognised.  His role in the rediscovery of Epicurus and revival of the ideas of the ancient Greek skeptics has led to claims that he had sympathies with atheism and libertinism.  The former is almost certainly untrue and the latter unlikely.  After his death, French and English translations of his work (he wrote in Latin) enhanced his reputation and for several generations his ideas continued to spread, finding their way into the curriculum of educational institutions in France, England, Italy and even North America.

Note: references to Casanova’s memoirs relate to the revised unabridged Arthur Machen English translation (Gutenberg project)

Dave Thompson (2018)


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