We’ve all heard of the term “public domain.” But what does it mean and how does it relate to intellectual property? The public domain can be thought of as everything that belongs to the public, rather than to any one person — things the public is free to use without encumbrance or having to pay a fee or being at risk of a lawsuit.

My car belongs to me and I’m free to use it, but the public is not; that is not part of the public domain. Knowledge gained by academic researchers or long long-known to everyone is part of the public domain. We can all use that knowledge without paying anyone a fee or even any legal requirement to acknowledge the source of the information. That is public domain.

An expired patent is, by legal definition, part of the public domain — that is, the technology disclosed in the patent(s) and any inventions claimed in the patent, once the patent is expired, become part of the public domain as part of an exchange between the patent owner and the public for the exclusive rights the patent owner temporarily enjoyed.

Likewise, there are other things that are in the public domain that “belong” to the public, such as free use of the language in communicating among ourselves. It would be improper and terribly burdensome on public behavior in public discourse if someone could trademark a word or a phrase that everyone is already using and say “now this belongs to me and to my product and, if you use it, I will sue you.” That makes no sense for a good reason.

Sometimes people ask or ponder what qualifies someone to get a patent or what qualifies someone to get a trademark or copyright. The answer is usually somewhat instinctive:  It needs to be something they created.

It can’t be something that has already been around for a long time without that person’s contribution. This kind of instinctual analysis inherently reflects a notion that whatever has recently been created and has value is not part of the public domain and could at least theoretically belong to one person or one owner. It is a very important part of intellectual property theory that, once something is in the public domain, intellectual property rights should never be allowed to take it back out.

This is the essence behind banning trademarks on any generic term, and it is also the essence of only permitting patents on things that are new. So when a patent examiner is given a new application to review and determine whether the things that are being claimed are really patentable, he or she looks at the “prior art” — which is really just published information about what is already in the public domain. Part of the process of patent examination is to identify whatever in the public domain is closest to what is being claimed as an invention and, if it is too close, the patent examiner rejects the claims. So, in this way of looking at things, the patent examiner is protecting the public domain from encroachment by a patent applicant.

Of course, in some Industries, the actual public domain and that part of it which is recorded in printed publications are not very much alike. A great example of this is the marijuana industry. If the public domain is everything that has been known or done or discussed or existed or sold for a long enough duration that no one can argue that it is still their own unique secret, that’s public domain — even if those commercial activities or discussions or knowledge in the relevant sector of the public were never published. In the case of marijuana, it is, of course, the case that the lack of publication was associated with the illegality of the activities.

Now that the activities are no longer illegal in many jurisdictions and people are applying for patents, we face a unique challenge in which the patent examiners look to the public domain, as defined by printed publications, and don’t see evidence that is clear about whether a particular patent claim is new or not. On the other hand, people who been working in the industry for a long time are very well aware of things that were openly known in the industry but that were never published. Therefore, particularly in the situation of marijuana patenting, there is a very large disconnect between what is in the “real” public domain and what is in the ”printed/published” public domain.

Coming back to the more general concept, the message is that people really can at least start my trusting their instincts about whether something should be protected over by a trademark or a patent or a copyright or a trade secret. Is it really new, or does it already belong to the public? That’s the question. The answer gives us a good starting point for discussing whether something should be protectable in an intellectual property system.