Forcing Patent Claims

AuthorChiang, Tun-Jen

Introduction

One of the oddest features of the patent system is that patentees get to draft the patent "claim."1 Because the patent claim defines the scope of the monopoly,2 patentees have a strong incentive to subtly slant the claim's language in a way that aggrandizes their rights to the detriment of the public. Moreover, it is impossible for the Patent and Trademark Office ("PTO") to police patentees so fully as to detect every subtle drafting trick.3 In short, it would seem a good idea to prohibit patentees from drafting claims and instead give claim-drafting power to a neutral entity such as the PTO or a court.

Much of the literature on patent-claim construction can be understood as implicitly criticizing the allocation of drafting power to patentees, although no one has done so explicitly.4 The existing literature on claim construction focuses on what I call the linguistic indeterminacy thesis-the argument that the problem with patent claims is their linguistic ambiguity and that such ambiguity results in overbroad patent rights.5 But as I have explained in a prior article with Lawrence Solum,6 patent claims are not especially ambiguous, and, in any case, ambiguous claims would not obviously lead to systematically overbroad patent rights since ambiguity can be construed either broadly or narrowly. Properly understood, the critics' real concern is not that claims are ambiguous but that self-serving patentees draft the claims in an overbroad manner.7 In other words, the critics implicitly argue that patentee-drafted claims are nothing more than self-serving statements entitled to no weight. Viewed in this light, the question becomes the following: Why does the patent system require patentees to draft claims? And what is the social value of patentee-drafted claims?

This Article provides an answer: patentee-drafted claims are socially valuable because they force patentees to disclose an imperfect approximation of the correct scope of a patent.8 Although patentees will overclaim, they cannot overclaim too much,9 and some degree of overbreadth is tolerable compared to the alternative. Namely, the only obvious alternative to relying on patentee-written claims is for some governmental entity, such as the PTO or a court, to determine the correct scope of a patent in the first instance. And a central premise of having a patent system at all (rather than some alternative incentive mechanism such as a government-sponsored prize system) is that the government lacks sufficient information to determine the correct level of reward for particular innovations.10 In other words, the only alternative to relying on somewhat overbroad patentee-drafted claims is for judges to hazard almost completely arbitrary guesses about optimal patent scope.* 11

This insight has important implications for the long-running debate over claim construction. Many commentators argue that, because claim text often does not describe the real invention, courts should use their interpretative powers to overcome this defect.12 In its extreme form, the argument holds that courts should abolish claims altogether and look only at external evidence (i.e., evidence outside the claim, such as the patent specification or expert testimony) to determine the real invention.13 In a less extreme form, the argument is that, although courts need not abolish claims, they nonetheless should give external evidence greater weight in the interpretative calculus in order to compensate for the patentee's drafting bias and to obtain the most accurate determination of the real invention.14 As this Article will explain, both of these arguments turn the problem on its head: the critics implicitly assume that courts can reliably discern the real invention (i.e., the optimal patent scope)15 without claims, but the whole reason that claims are required is that courts lack the capacity to perform this function.

The information-forcing insight's initial implication is that courts should refrain from abolishing claims altogether and from attempting directly to discern optimal patent scope; such a methodology faces the problem of insurmountable information costs. But the information-forcing insight has another implication: if courts did not give patentee-written claim text any more weight in claim construction than other types of evidence, then patentees would have no incentive to spend money to draft claims.16 The long-term result would be de facto abolition, which would once again increase judicial information costs.

The result of this analysis is that courts must delicately balance two competing considerations. In the short run, giving weight to both claim text and external evidence will generate the best outcomes, as courts can reap the information benefits of claim text while also using external evidence to detect and rectify a particular patentee's drafting bias. In the long run, however, courts cannot rely too heavily on external evidence, because a patentee's incentive to write claims, and to write them in an informative manner, would disappear if courts gave claim text too little weight. As a result, courts must balance the short-term desire to achieve better outcomes (the equal-weight approach) against the long-term need to preserve incentives for patentee claim drafting (the more-weight-to-claim-text approach). And such a balancing act reflects real life, where courts give primary weight to claim text-by treating the written claim as a presumptive baseline for patent scope-but also do not exclude external evidence from the analysis completely.17 This Article therefore provides a normative and descriptive theory for how courts should and do construe patent claims.

The Article proceeds in four Parts. Part I provides a background and describes the puzzle of allowing patentees to write patent claims, as well as explains the adverse consequences (and implicit criticisms) that allocating drafting responsibility in this way has produced. Part II then explains why allocating drafting responsibility to patentees is an efficient mechanism to solve an underlying information problem. Part III elaborates on a key implication of the theory-i.e., that in order to provide an incentive for patentees to draft claims and to convey accurate information, courts must give claim text some weight over external evidence, a position that contradicts many academic proposals. Part IV then addresses some objections, and a brief conclusion follows.

  1. The Puzzle of Patentee-Drafted Claims

    1. Background on the Patent Document

      A U.S. patent is a complex document, but its two most important parts are the specification and the claims.18 The patentee drafts both the specification and the claims, and both are supposed to describe the patentee's invention. 19 Although the Patent Act uses the word "invention" in both of these contexts, the term refers to two distinct concepts. As this Section will explain, the specification describes an invention in the sense of an embodiment, while the claim describes an invention in the sense of monopoly scope.

      1. The Specification Describes an Embodiment

        In simplified terms, the specification is the portion of the patent that provides technical knowledge about the invention. It is obviously important that the disclosure is sufficiently detailed to enable the public to gain the full benefit of the invention once the patent expires.20 Accordingly, § 112 of the patent statute mandates that the specification "contain a written description of the invention, and of the manner and process of making and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art . . . to make and use the same."21

        In practical terms, this means that the specification describes an embodiment. 22 Only tangible embodiments can be "made," and so the statute implicitly conceptualizes the "invention" of the specification in these terms. Similarly, the requirement that the specification description be detailed and "exact" reflects a conception of the invention as a tangible embodiment whose precise features can be specified. This is not to say that the embodiment actually needs to be built or that the specification is confined to a single embodiment-specifications often describe several embodiments that are not actually reduced to practice. The point is that the specification describes a fixed set of concrete things that all could be reduced to physical form at the time of patent filing-rather than an abstract principle or idea that intrinsically lacks such concreteness.

        For example, the Wright brothers could not have simply written in their patent specification that they had invented "a flying machine with wings." Such an abstract description would have been too sparse to satisfy the requirements of § 112.23 Rather, the Wright brothers had to specify that their particular airplane embodiment had a wooden frame and cloth wings, that it was controlled using rope pulleys, and numerous other details about their particular wooden glider.24 Such a concrete and detailed description serves the goals of the patent system by ensuring that the public has all the technical details it needs to reproduce the patentee's embodiment in the future.

      2. The Claim Delineates Monopoly Scope

        Although it is important that patentees provide extensive technical detail about their inventions, the law has long recognized that patent scope cannot be limited to literal replication of the specification embodiment or embodiments.25 If the scope were so limited, copyists would quickly take the patentee's core idea but make minor changes to the details, thereby escaping infringement.26 For example, the Stone Age inventor of the table might disclose a table embodiment made of wood in the patent specification, but he could not disclose a plastic table because plastic would not have been invented. After plastic (or some other material besides wood) was invented, however, anyone who saw a...

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