The Italian philosopher of nature Bernardino Telesio (1509-1588) was a leader in the Renaissance movement against medieval Aristotelianism.

Bernardino Telesio was born in Cosenza near Naples. He came from a noble family and received his early education in Milan under the instruction of his humanist uncle, Antonio Telesio. He completed his formal education by studying at Rome and then at Padua, where he was awarded his doctor's degree in 1535. The next few years of his life were spent in a monastery. This was only temporary, however, since he married in 1553. Beginning in 1545, he lived primarily in Naples or nearby at Cosenza. He was responsible for the establishment of an academy in Cosenza consecrated to the study of natural philosophy and based on his ideas and methods. Although Telesio did little teaching at this academy, he did have several pupils who continued the foundation after his death, which occurred in Cosenza in October 1588.

Telesio's most important work, in which his chief naturalistic ideas are advanced, is De rerum natura iuxta propria principia. Although the first part of this work was published in 1565, the work was not completed until 1586. In this book Telesio attacked both the method and content of Aristotelian philosophy. The Aristotelians, he felt, relied too much on reason and too little on the senses. Telesio's own emphasis on the use of the senses to reach natural truth led to the conclusion that knowledge is derived from the senses. In his attack on the content of Aristotelian philosophy, Telesio discarded the Aristotelian doctrine of matter and form. In its place, he argued that all things in nature are based on three principles: matter, which is inert and corporeal; the two natural forces of heat and cold, which are incorporeal and active; and the interaction or conflict of these forces, heat and cold, operating on corporeal, inert matter. From the fluctuating degrees of conflict arise the different types of existence. Although others pointed to contradictions in Telesio's thought, he is still an important figure in the transition from the Aristotelian emphasis on reason and the principle of authority to the modern scientists' emphasis on experiment and independent investigation and observation of nature.