Bachelard was a rationalist in the Cartesian sense, although he recommended his "non-Cartesian epistemology" as a replacement for the more standard Cartesian epistemology. He compared "scientific knowledge" to ordinary knowledge in the way we deal with it, and saw error as only illusion: "Scientifically, we think the truth as the historical rectification of a long error, and we think experience as the rectification of the common and original illusion (illusion première).
The role of epistemology is to show the history of the (scientific) production of concepts; those concepts are not just theoretical propositions: they are simultaneously abstract and concrete, pervading technical and pedagogical activity. This explains why "The electric bulb is an object of scientific thought… an example of an abstract-concrete object." To understand the way it works, one has to pass by the detour of scientific knowledge. Epistemology is thus not a general philosophy that aims at justifying scientific reasoning. Instead it produces regional histories of science.
In addition to epistemology, Bachelard's work deals with many other topics, including poetry, dreams, psychoanalysis, and the imagination. The Psychoanalysis of Fire (1938) and The Poetics of Space (1958) are among the most popular of his works.
Book Review from Amazon:
Writing a preface for The Poetics of Space (1958) in 1963, a year after his friend's death, medievalist Etienne Gilson noted: "We all loved him, admired him and envied him a little, because we felt he was a free mind, unfettered by any conventions either in his choice of the problems he wanted to handle or in his way of handling them."
Gilson goes on to say that this book, The Psychoanalysis of Fire (1938), was Bachelard the free mind's "first warning shot." He records the puzzlement he had upon its publication in these words: "After appointing a man to teach the philosophy of science and seeing him successfully do so for a number of years, we don't like to learn that he has suddenly turned his interest to a psychoanalysis of the most unorthodox sort, since what then was being psychoanalyzed was not even people, but an element."
As one of the truly unusual and original books anyone would hope to come upon, almost every paragraph (nay, sentence) of the book has the power to change the perspective of an engaged reader. Perspective on, yes, fire, but also on many other things. Prometheus and his "clever disobedience," which leads to a startling formulation "The Prometheus complex is the Oedipus complex of the life of the intellect." The psychoanalysis of rubbing (thus, cleaning) and heat producing in what Bachelard calls the "Novalis complex," which leads to a meditation on the nature of love. Alcohol, the eau-de-feu ("water on fire") working as eau-de-vie by setting one's being on fire instantaneously in the "Hoffmann complex." These are just most obvious themes of the book. Attentive readers will discover much, much more to cherish.
After my encounter with Bachelard, I was often awed to find myself responding to things so very differently, be it reading literature/philosophy, or everyday chores such as doing dishes and cooking. You will, for instance, never read Poe in the same way. While his most unforgettable essay on Poe appears in Water and Dreams (1942), this book too has excursions to him here and there.