What does the “on-sale bar” prevent?

The on-sale bar is a critical principle in patent law that prevents an inventor from obtaining a patent if their invention was sold or offered for sale more than one year prior to the filing date of the patent application. Specifically, if an invention is put on sale or is publicly available before an application is filed, it can compromise the ability to patent that invention. This rule was established to encourage inventors to seek patent protection in a timely manner and to prevent the commercialization of inventions that aren't legally protected, thereby maintaining the integrity and novelty of the patent system.

In this context, the on-sale bar serves to ensure that the public can access information about inventions and products that are in the marketplace. If an invention is widely available for commercial use, it may lose its novelty and not meet the criteria necessary for patentability. Therefore, if an invention was on sale more than one year prior to filing, it cannot be patented, reinforcing the importance of filing an application promptly after an invention is made.