A more useful way of separating science from art is available to us. Both art and science endeavor to reveal the truths about human existence, but they differ in their methodology. Science, once divorced from philosophy (as evidenced by the rise of Francis Bacon and the decline of Aristotle), imposed a sense of order on its investigation of nature. Borrowing from Pythagoras and Euclid a healthy respect for logical proof, science proceeds by linking theory to observation, such that the principle of verification now provides a solid rational foundation upon which science can transform theory into fact. Here is where Freud runs into difficulty. To gain entry into the halls of science, your theory must not only be stimulating, but it needs the support of experimental data. Freud's theory of the unconscious and his explanations of human behavior, though highly stimulating and provocative, have never been verified by experimental data.
In fact, it is difficult to see how it ever could be. Even with the advantages of new technology, no one can detect the presence of the "unconscious" any more than a CAT scan will reveal the presence of a human soul. But Freud's work is based largely on his early clinical practice in which he made careful observations of patients over a period of months and sometimes years. As a result of his work, analyzing the dreams of patients, he came to infer the existence of something he would eventually call the "unconscious." Thus, his work is supported by inferential data (i.e., in a court of law, "circumstantial" evidence) but not by direct observation of the facts. Freud only had access to whatever "facts" the patient could give him. The human psyche, after all, does not lend itself to the same empirical tests as a model of gravitational force. Whereas, Newton succeeded in quantifying gravity in a way that left no doubt as to its veracity. Yet this certainty of proof continues to elude the field of psychiatry. The best that can be said of psychoanalysis is that sometimes patients improve from the treatment, and sometimes they do not. Of course, this is also true of cancer patients, but with MRI scans and toxicology we can positively identify cancerous cells. We are much less confident about the workings of the human mind. Nevertheless, since Freud, psychiatry today has managed to find acceptance by the medical community and is considered to be a bit more like science than astrology. But it still has a long way to go.