While the public domain is a pervasive concept in intellectual property law, it is hardly a robust one. Surprisingly little attention has been given to the public domain in the statutes establishing and regulating intellectual property, in the case law interpreting these statutes or concerning the common law of intellectual property, or in the scholarly literature, at least until recently. Public domain would appear to be a minimalist concept indicative of the negative legal conclusion that something is not protectable or protected under the law. Accordingly, something is either protected (i.e., in the private domain) or unprotected (i.e., in the public domain). Something may be in the public domain because it is unprotectable (i.e., it does not fall within a protectable category of intellectual property; “the law just does not spread its protection so far”). In addition, something may be in the public domain although it fits within a particular title of intellectual property because it is unprotected, i.e.: (i) protection has not been sought; (ii) if protection is sought, the subject matter fails to satisfy formal or substantive requirements for protection; or (iii) if protection is sought and obtained, the protection has terminated (e.g. by expiration, abandonment, invalidity). In short, a presumably discernable dichotomy is drawn between the private and public domains, with the fundamental distinction being that subject matter in the latter domain is available to all while that in the former is subject to the control of the owner.

Under such a dichotomy, the public domain may be impacted in a number of ways. First, the categories of subject matter that are protectable may be expanded (e.g. reclassifying certain subject matter from unprotectable to protectable status; protecting newly discovered or developed subject matter). This would delay such subject matter from entering the public domain if protection is sought and obtained. A second means would be to lower the standards for protection (formal and/or substantive) with respect to protectable subject matter. Thus, subject matter now protectable at a lower standard, that would have previously entered the public domain, is delayed from entering. Delays in entering a public domain may also be achieved by extending the term for which protection is granted or by resuscitating works whose protection had terminated. Finally and perhaps more seriously, the public domain may also be impacted if subject matter protected under one form of intellectual property upon termination of that form may continue to be protected under another form of intellectual property for an extended term.

All of the foregoing impactions are current today to the correlative benefit of the private domain: there has been an expansion of protectable subject matter in all areas of intellectual property. The duration of protection has been increased for certain titles. Certain terminated copyrights have been given new life. There are certain indications that lower substantive standards of protection are being applied. There is overlapping protection of the same subject matter by different forms of intellectual protection delaying full entrance of that subject matter into the public domain.

Accordingly, there is increasing concern among those constituencies who rely upon intellectual subject matter. To these, any hindrance to full access to intellectual subject matter of whatever nature may be disconcerting (if not tragic) whether the access is desired for commercial ends, or for purely academic, artistic or philosophical pursuits. Professor Lessig laments the insidious assault on the public domain: “So invisible is public domain that we don't even see it when it is everywhere around; so invisible is the idea that the free might matter to creativity, that when it is enclosed, we are convinced this is progress.” On the other side are those producers and owners of intellectual subject matter who urge expanded intellectual property protection, insisting that sufficient incentives must be provided to ensure an adequate supply of intellectual creations that will redound to the benefit of society as a whole. As well put by Professor Samuelson: “Whether the public domain is a virtual wasteland of undeserving detritus or the font of all new creation is the subject of some debate.”

In this article, the concept of public domain will be addressed as generally as possible. The basic premise is that the public domain serves primarily as a source of sensory stimuli (which will be termed the “public-domain-as-stimuli” thesis) and only secondarily as some sort of “intellectual commons,” where all may freely exploit its contents. As an introduction to this thesis, in Part II, legal and philosophical justifications for the thesis will be introduced. Then the “creative cognitive process” will be outlined to illustrate how human intervention though this process, in response to stimuli from the public domain, transforms and transports subject matter from the public domain to the private domain. In Part III, the dichotomy between the public and private domain will be considered in a “state-of-nature” model before the introduction of an intellectual property system. According to this model, in response to stimuli in the public domain and as a consequence of the creative cognitive process of the responding individual, an “idea” is formed in the mind of that individual. For want of a better definition we can use John Locke's: “Idea is the object of thinking.” This idea is privatized (i.e., is in the private domain) by virtue of being secret. The loss of secrecy transfers the result of the creative process to the public domain.

The modifications to the basic model necessitated by the introduction of an intellectual property system will be addressed in Part IV, including the expansion of the private domain to include a “strong version” of protection under various titles of intellectual property in addition to the “weak version” implemented by secrecy. The public domain will also be compartmentalized to illustrate a “weak version,” whose function is to serve as a source of stimuli for the creative process, and a “strong version,” which would also permit public exploitation in the absence of extant intellectual property protection. In Part V, the public-domain-as-stimuli thesis will be examined within the various forms of intellectual property and any differences identified among them. Because certain intellectual subject matter is unprotectable in a strong version, consideration will be given in Part VI to the nature of this subject matter (“unprotectables”) in the context of the public-domain-as-stimuli thesis. Finally, some conclusions are drawn concerning modifications in the intellectual property system as suggested by the public-domain-as-stimuli thesis.