An invention is conceived when a definite and permanent idea of an operative invention is known. Conception under patent law is complete when one of ordinary skill in the art could make the invention without undue research or experimentation.
Prior to the Leahy–Smith America Invents Act (AIA), the second person to file a patent application disclosing an invention is awarded the patent over the first to file if said second person can prove a date of conception prior to the date of conception by the first to file, coupled with diligence in pursuing the invention until the filing date of the second-filed patent application.
However, under the new 2013 patent law, conception of invention has been largely replaced by a race to the USPTO. The first inventor to file establishes ownership in the invention for patent awards.