This chapter details the practical, theoretical, and philosophical aspects of experimental science. It discusses how one chooses a project, performs experiments, interprets the resulting data, makes inferences, and develops and tests theories. It then asks the question, "are our theories accurate representations of the natural world, that is, do they reflect reality?" Surprisingly, this is not an easy question to answer. Scientists assume so, but are they warranted in this assumption? Realists say "yes," but anti-realists argue that realism is simply a mental representation of the world as we perceive it, that is, metaphysical in nature. Regardless of one's sense of reality, the fact remains that science has been and continues to be of tremendous practical value. It would have to be a miracle if our knowledge and manipulation of the nature were not real. Even if they were, how do we know they are true in an absolute sense, not just relative to our own experience? This is a thorny philosophical question, the answer to which depends on the context in which it is asked. The take-home message for the practicing scientist is "never assume your results are true."

The seventeenth-century microscopists Robert Hooke and Henry Power sought to rhetorically establish the truthfulness of the visual images produced by their instruments, but a counter-rhetoric of visuality was established by Margaret Cavendish in Observations upon Experimental Philosophy (1666). The microscopists’ belief that magnification revealed the truth of nature ran counter to Cavendish’s probabilistic belief that no individual could grasp the infinite truth of nature and sought explanations from the superficies of observed objects rather than the ‘interior figurative motions’ which Cavendish saw as the universal cause of all natural phenomena. While the microscopists emphasized the aesthetic beauty of the micro-visible world, Cavendish emphasized its monstrosity: for her the truth could only be perceived by the ‘natural’ eye observing things in their unmagnified state. Exploiting the microscopists’ complaints about the variability of their images and the defects of their instruments Cavendish redefines the microscopic image as definitively outside the ‘real’.

Many of Cicero’s translations of Greek concepts (assent, comprehension, quality) have become common terms in philosophy but also in ordinary language in many European countries. Some of them, pertaining to epistemology, ethics, or physics, are studied in this chapter to show why and how Cicero set out to create a Latin philosophical vocabulary. He wanted to extend the supremacy of Rome to an area formerly reserved to the Greeks. He tried to avoid technical terms or neologisms and preferred open notions to closed concepts. He aimed at conveying the complexity of Greek philosophical doctrines in Latin and sometimes brought out certain nuances which did not exist in the Greek terms (as in the case of probabile). Cicero’s originality as a philosopher does not lie in creating a new system but in providing philosophy with a new language and in promoting the idea that philosophy was not the privilege of Greek culture but a field open to human ingenuity.