California has become a Daubert state. In Sargon v. The University of Southern California, the California Supreme Court held that judges are the “gatekeepers” with regard to expert or scientific evidence in this state, just as has been the case in the federal system (and many other states) since the decision in Daubert. Now that California is avowedly a Daubert state, it is important to understand why courtroom evidence – scientific, expert or, for that matter, otherwise – is properly grounded in empiricism. Empiricism is the theory that knowledge is derived from experience. Understanding this empirical basis for both Daubert and Sargon will help guide the judge in her role as “gatekeeper” as those cases require. The practical effect is to limit the actual evidence that can come in, not just case-by-case, but in terms of the nature of some types of previously admitted testimony. Non-empirical conclusions – or explanations for reaching those conclusions – are no longer admissible in California.