Optics of Thomas Hobbes
- Born:
- April 5, 1588, Westport, Wiltshire, England
- Died:
- December 4, 1679, Hardwick Hall, Derbyshire (aged 91)
Hobbes’s most significant contributions to natural science were in the field of optics. An optical theory in his day was expected to pronounce on the nature of light, on the transmission of light from the Sun to the Earth, on reflection and refraction, and on the workings of optical instruments such as mirrors and lenses. Hobbes took up these topics in several relatively short treatises and in correspondence, including with Descartes on the latter’s Dioptrics (1637). The most polished of Hobbes’s optical works was A Minute or First Draught of the Optiques (1646).
In its mature form, Hobbes’s optical theory held that the dilations and contractions of an original light source, such as the Sun, are transmitted by contact with a uniform, pervading ethereal medium, which in turn stimulates the eye and the nerves connected to it, eventually resulting in a “phantasm,” or sense-image, in the brain. In Hobbes’s theory, the qualities of a sense-image do not need to be explained in terms of the qualities of a perceived object. Instead, motion and matter—the motion of a light source, the disturbance of a physical nervous system, and sensory membranes—are all that have to be invoked. In contrast, traditional optics—optics as developed within Aristotle’s framework—had held that seeing the colour of something—the redness of a strawberry, for example—was a matter of reproducing the “form” of the colour in the sense organs; the form is then abstracted from the sense organs by the mind. “Sensible forms,” the characteristic properties transmitted by objects to the senses in the act of perception, were entirely dispensed with in Hobbes’s optics.
Hobbes’s system
Theories that trace all observed effects to matter and motion are called mechanical. Hobbes was thus a mechanical materialist: He held that nothing but material things are real, and he thought that the subject matter of all the natural sciences consists of the motions of material things at different levels of generality. Geometry considers the effects of the motions of points, lines, and solids; pure mechanics deals with the motions of three-dimensional bodies in a full space, or plenum; physics deals with the motions of the parts of inanimate bodies insofar as they contribute to observed phenomena; and psychology deals with the effects of the internal motions of animate bodies on behaviour. The system of the natural sciences described in Hobbes’s trilogy represents his understanding of the materialist principles on which all science is based.
The fact that Hobbes included politics as well as psychology within his system, however, has tended to overshadow his insistence on the autonomy of political understanding from natural-scientific understanding. According to Hobbes, politics does not need to be understood in terms of the motions of material things (although, ultimately, it can be); a certain kind of widely available self-knowledge is evidence enough of the human propensity to war. Although Hobbes is routinely read as having discerned the “laws of motion” for both human beings and human societies, the most that can plausibly be claimed is that he based his political philosophy on psychological principles that he thought could be illuminated by general laws of motion.
Last years and influence
Although he was impugned by enemies at home, no Englishman of the day stood in such high repute abroad as Hobbes, and distinguished foreigners who visited England were always eager to pay their respects to the old man, whose vigour and freshness of intellect remained unquenched. In his last years Hobbes amused himself by returning to the classical studies of his youth. The autobiography in Latin verse with its playful humour, occasional pathos, and sublime self-complacency was brought forth at the age of 84. In 1675 he produced a translation of the Odyssey in rugged English rhymes, with a lively preface, “Concerning the Virtues of an Heroic Poem.” A translation of the Iliad appeared in the following year. As late as four months before his death, he was promising his publisher “somewhat to print in English.”
Hobbes’s importance lies not only in his political philosophy but also in his contribution to the development of an anti-Aristotelian and thoroughly materialist conception of natural science. His political philosophy influenced not only successors who adopted the social-contract framework—John Locke, Jean-Jacques Rousseau, and Immanuel Kant, for example—but also less directly those theorists who connected moral and political decision making in rational human beings to considerations of self-interest broadly understood. The materialist bent of Hobbes’s metaphysics is also much in keeping with contemporary Anglo-American, or analytic, metaphysics, which tends to recognize as real only those entities that physics in particular or natural science in general presupposes.
Tom Sorell