Bernardino Telesio (1509 - 1588) was an Italian philosopher and natural scientist.
Telesio was born of noble parentage in Cosenza, a city in Calabria, Southern Italy. He was educated in Milan by his uncle, Antonio, himself a scholar and a poet of eminence, and afterwards in Rome and Padua. His studies included all the wide range of subjects, classics, science and philosophy, which constituted the curriculum of the Renaissance savants. Thus equipped, he began his attack upon the medieval Aristotelianism which then flourished in Padua and Bologna. He began to lecture in Naples and eventually founded the Cosentian Academy in 1511. In 1563, or perhaps two years later, appeared his great work De Rerum Natura Iuxta Propria Principia (On the Nature of Things according to their Own Principles), which was followed by a large number of scientific and philosophical works of subsidiary importance. The heterodox views which he maintained aroused the anger of the Church on behalf of its cherished Aristotelianism, and a short time after his death his books were placed on the Index.
Telesio was the head of the great Southern Italian movement which protested against the accepted authority of abstract reason, and sowed the seeds from which sprang the scientific methods of Tommaso Campanella and Giordano Bruno, of Francis Bacon and René Descartes, with their widely divergent results. He, therefore, abandoned the purely intellectual sphere and proposed an inquiry into the data given by the senses, from which he held that all true knowledge really comes (his theory of sense perception was essentially a reworking of Aristotle's theory from De Anima). Instead of postulating matter and form, he bases existence on matter and force. This force has two opposing elements: heat, which expands, and cold, which contracts. These two processes account for all the diverse forms and types of existence, while the mass on which the force operates remains the same. The harmony of the whole consists in this, that each separate thing develops in and for itself in accordance with its own nature while at the same time its motion benefits the rest. The obvious defects of this theory, (i) that the senses alone cannot apprehend matter itself, (2) that it is not clear how the multiplicity of phenomena could result from these two forces, thought it is no less convincing than Aristotles hot/cold, dry/wet explanation, and (3) that he adduced no evidence to substantiate the existence of these two forces, were pointed out at the time by his pupil, Patrizzi.
Moreover his theory of the cold earth at rest and the hot sun in motion was doomed to disproof at the hands of Copernicus. At the same time, the theory was sufficiently coherent to make a great impression on Italian thought. It should be mentioned, though, that his obliteration of a distinction between superlunar and sublunar physics was certainly quite prescient though not acknowledged by his successors as particularly worthy of note. When Telesio went on to explain the relation of mind and matter, he was still more heterodox. Material forces are, by hypothesis, capable of feeling; matter also must have been from the first endowed with consciousness. For consciousness exists, and could not have been developed out of nothing. This leads him to a form of hylozoism. Again, the soul is influenced by material conditions; consequently the soul must have a material existence. He further held that all knowledge is sensation ("non ratione sed sensu") and that intelligence is, therefore, an agglomeration of isolated data, given by the senses. He does not, however, succeed in explaining how the senses alone can perceive difference and identity. At the end of his scheme, probably in deference to theological prejudices, he added an element which was utterly alien, namely, a higher impulse, a soul superimposed by God, in virtue of which we strive beyond the world of sense. This divine soul is hardly a completely novel concept if viewed in the context of Averroestic or Thomasian perceptual theory.
The whole system of Telesio shows lacunae in argument, and ignorance of essential facts, but at the same time it is a forerunner of all subsequent empiricism, scientific and philosophical, and marks clearly the period of transition from authority and reason to experiment and individual responsibility. Beside the De Rerum Natura, he wrote De Somno, De his guae in acre fiunt, De Mari, De Comelis et Circulo Lactea, De usu respirationis, etc.
Telesio writes in the beginning of the Proem of the first book of the third edition of De Rerum Natura Iuxta Propria Principia Libri Ix... "That the construction of the world and the magnitude of the bodies contained within it, and the nature of the world, is to be searched for not by reason as was done by the ancients, but is to be understood by means of observation." (Mundi constructionem, corporumque in eo contentorum magnitudinem, naturamque non ratione, quod antiquioribus factum est, inquirendam, sed sensu percipiendam.) This statement, found on the very first page, summarizes what many modern scholars have generally considered to be Telesian philosophy, and it often seems that many did not read any further for on the very next page he sets up his hot/cold theory of informed matter, a theory that is clearly not informed by our modern idea of observation. For Telesio, observation (sensu percipiendam) is a much larger mental process than simply recording data, observation also includes analogical thought.
Though Francis Bacon is generally credited nowadays with the codification of an inductive method that wholeheartedly endorses observation as the primary procedure for acquiring knowledge, he was certainly not the first to suggest that sensory perception should be the primary source for knowledge. Among natural philosophers from the Renaissance, this honor is generally bestowed upon Telesio. Bacon himself acknowledges Telesio as being "the first of the moderns" (De Telesio autem bene sentimus, atque eum ut amantem veritatis, & Scientiis utilem, & nonnullorum Placitorum emendatorem & novorum hominum primum agnoscimus., from Bacon's De principiis atque originibus) for putting observation above all other methods for acquiring knowledge about the natural world. This frequently quoted phrase from Bacon, though, is misleading, for it oversimplifies and misrepresents Bacon’s opinion of Telesio. Most of Bacon's essay is an attack on Telesio and this phrase, invariably taken out of context, has facilitated a general misconception of Telesian natural philosophy by giving to it a Baconian stamp of approval, which was far from Bacon’s original intentions. Bacon sees in Telesio an ally in the fight against ancient authority, but he has little positive to say about Telesio's specific theories.
What is perhaps most striking about De rerum natura is Telesio's attempt to mechanize as much as possible. Telesio clearly strives to explain everything in terms of matter informed by hot and cold and to keep his arguments as simple as possible. When his discussions turn to human beings he introduces an instinct of self-preservation to account for their motivations. And when he discusses the human mind and its ability to reason in the abstract about immaterial and divine topics, he adds a soul. For without a soul, all thought, by his reasoning, would be limited to material things. This would make God unthinkable and clearly this was not the case, for observation proves that people think about God.
Telesio can be seen as a Stoic, an Epicurean, a Parmenidian, and even though he resists the ideas of Aristotle with vigor, his overall theory is quite Aristotelian. He may have felt that he was overturning the Aristotelian worldview and in his own time his views may have been perceived as radical, but from today's perspective he seems very endebted to Aristotle.