[T]hat which I am now entering upon being the Consideration of the things themselves whereinto Spagyrists resolve mixt Bodies by the Fire, If I can s… - Robert Boyle

Not that I at all disallow the use of reasoning upon experiments, or the endeavouring to discern as early as we can the confederations, and differences, and tendencies of things: for such an absolute suspension of the exercise of reasoning were exceeding troublesome, if not impossible. And, as in that rule of arithmetic, which is commonly called by proceeding upon a conjecturally-supposed number, as if it were that, which we inquire after, we are wont to come to the knowledge of the true number sought for; so in physiology it is sometimes conducive to the discovery of truth, to permit the understanding to make an hypothesis, in order to the explication of this or that difficulty, that by examining how far the phænomena are, or are not, capable of being solved by that hypothesis, the understanding may, even by its own errors, be instructed.

I find that even Eminent Writers (such as Raymund Lully, Paracelsus, and others) do so abuse the termes they employ, that as they will now and then give divers things one name, so they will oftentimes give one thing, many Names; and some of them (perhaps) such, as do much more properly signifie some Distinct Body of another kind; nay even in Technical Words or Termes of Art, they refrain not from this Confounding Liberty; but will, as I have Observ'd call the same Substance, sometimes the Sulphur, and Sometimes the Mercury, of a Body.

And that you may know... what kind of writings I mean, I shall name to you the learned Gassendus his little Syntagma of Epicurus's philosophy, and that most ingenious gentleman Monsieur Descartes his principles of philosophy. For though I purposely refrained, though not altogether from transiently consulting about a few particulars, yet from seriously and orderly reading over those excellent (though disagreeing) books, or so much as Sir Francis Bacon's Novum Organum, that I might not be prepossessed with any theory or principles, till I had spent some time in trying what things themselves would incline me to think; yet beginning now to allow myself to read those excellent books, I find by the little I have read in them already, that if I had read them before I began to write, I might have enriched the ensuing essays with divers truths, which they now want, and have explicated divers things much better than I fear I have done.