Who was first?

Remember that we said a patent may be granted to the first person to invent something (at least, under the First to Invent system). But how do you know who was first? In the United States, when two or more Inventors claiming essentially the same invention file applications, a proceeding called an Interference is conducted to determine who the first inventor is. The first inventor must be able to prove his case with appropriate evidence like laboratory records, logbooks etc. Therefore, even if the person who filed later is found to have invented earlier, he would be considered the first inventor. This is where an extremely important concept in patents becomes important: the Priority Date. The priority date is the earliest date that the inventor can prove he conceived of an invention (it actually gets a bit more complicated than that, but that definition will suffice for our purposes).

How does an inventor prove when an invention was first conceived? Well, this can get complicated if an argument of priority dates goes to court. They might consider all kinds of evidence, including witness testimony, lab notebooks, etc. But for most purposes it is simpler than that.

In general, the priority date is going to be the date that the patent application was filed. But, there are exceptions (and they are not infrequent - so be sure to check). These exceptions occur in a variety of circumstances including if a provisional application (which is a simplified application, largely designed just to prove an earlier priority date) was filed before the actual application, if the invention was first patented in another country (the inventor then gets to claim the priority date from the application he filed in the other country, since that proves the invention was invented earlier), or if the patent is a family member stemming from a Continuation in Part or a Divisional Application (in which case the new application normally gets to claim the priority date of the parent document).

So, hunt around at the top of the patent a bit. If you see dates listed that pre-date the application, or if information is present which indicates a Continuation in Part or a Divisional Application, the priority date is probably not the application date. Never, ever, assume the date the patent was issued is the priority date. You will always be wrong.

Understanding how to determine the priority date is very important in Validity Searches, as only prior art that pre-dates the priority date of the patent in question is relevant.