Patent applicants and inventors face an often overlooked challenge when drafting patent applications - satisfying the written description requirement under 35 USC § 112(a) of the U.S. Patent Code. This section, which governs the written description and enablement requirements, plays an important role in securing priority and ensuring your patent application holds up during prosecution.

Serving two key purposes - establishing priority for your invention and providing sufficient support for claims during prosecution – the legal landscape surrounding this requirement is complex, non-uniform, and highly fact-intensive.

Let’s break down what this section means in practice, why it’s often challenging, and what inventors, companies, and their patent counsel should keep in mind.

What Is 35 U.S.C. § 112(a), and Why Does It Matter?

35 USC § 112(a) requires, in relevant part, that your patent application:

• Contain a written description of the invention; and
• Do so in such full, clear, concise, and exact terms to enable any person skilled in the art to make and use the invention without undue experimentation.

Meeting this requirement is critical for two major reasons:

1. Establishing Priority: In the first-to-file system, your application must convincingly demonstrate that you were the first to invent. If your application fails the written description requirement, you could lose your priority date, particularly with respect to claims that are not supported in the priority document.
2. Supporting Claim Amendments During Prosecution: Patent prosecution is rarely a straight line. Rejections are common, and claim amendments are a frequent part of the process. But you can only amend your claims and the amendments accepted by an Examiner, if the application provides support for the amendment, e.g., if the application was drafted with future challenges in mind

The Written Description Legal Landscape Is Complex and Inconsistent

One of the biggest challenges with the written description requirement of 35 U.S.C § 112(a) is that the law is highly fact-dependent and non-uniform. Patent attorneys face seemingly contradictory outcomes from case law regarding what constitutes an adequate written description. Courts and examiners often interpret the requirement differently, depending on the invention, technology involved, and progress in the specific technological field.
For example:

• In one situation, one example of a compound might be enough to support a broader claim to a genus (In re Herschler, 591 F.2d 693, 697-98 (C.C.P.A. 1979)).
• In another, a single example is not sufficient, and a “representative number” of species is required (In re Gosteli, 872 F.2d 1008 (Fed. Cir. 1989); Abbvie Deutschland GmbH & Co. v. Janssen Biotech, Inc., 759 F.3d 1285, 1299 (Fed. Cir. 2014)), and courts have not provided clarity on what constitutes this “representative number.”

Some court decisions say you do not need working examples (LizardTech v. Earth Res. Mapping, Inc., 424 F.3d 1336, 1345 (Fed. Cir. 2005); Ariad Pharm., Inc. v. Eli Lilly & Co., 598 F.3d 1336, 1352 (Fed. Cir. 2010)), while others emphasize the importance of including examples and actual reduction to practice (Novozymes A/S v. DuPont Nutrition Biosciences APS, 723 F.3d 1336, 1350 (Fed. Cir. 2013)). Similarly, in some technologies, a broad conceptual description might suffice (Vas-Cath v. Mahurkar, 935 F.2d 1555, 1563 (Fed. Cir. 1991); Enzo Biochem, Inc. v. Gen–Probe, Inc. 323 F.3d 956, 964 (Fed. Cir. 2002)), while in others, especially emerging or unpredictable fields like biotechnology, a deep level of detail is expected. 

This inconsistency makes it nearly impossible to apply a single formula across all cases.

The Federal Circuit acknowledges this apparent tension between legal standards in the written description jurisprudence, stating that: “whatever inconsistencies may appear to some to exist in the application of the law, those inconsistencies rest not with the legal standard but with the different facts and arguments presented to the courts.”  See Ariad Pharm., Inc., 598 F.3d at 1352.
It is apparent that the written description analysis is highly fact-intensive and must be evaluated on a case-by-case basis.  This limits the precedential value of individual cases and creates significant challenges for patent drafters. 

Within the chemical art, the Federal Circuit would not set a bright light rule, and articulated its reluctance to do so, reasoning that “broadly articulated rules are particularly inappropriate in this area.  See In re Wertheim, 541 F.2d 257, 263 (C.C.P.A. 1976) for the proposition that “[b]roadly articulated rules are particularly inappropriate in this area.”  Citing to In re Smith, 458 F.2d 1389, 1394, (C.C.P.A. 1972)

How Inventors and Companies Should Handle the Written Description

Given this legal gray area, the best course of action is to engage with patent counsel early and often. As a client, you don’t need to know every nuance of Section 112(a), but you should ensure your legal team does.

Key questions to ask include:

• Does the application adequately describe the invention and any variations you may want to claim later?
• If you have one example, does the application provide enough structure-function rationale to support a broader genus?
• Has the application included sufficient examples to withstand scrutiny compared with other prosecuted patents in the industry?
• Are the specification, original claims, and drawings taking into consideration how the claims might need to be amended during prosecution or defended later in the event of a challenge to the validity of one or more claims?

Practical Implications: The Risks of an Inadequate Written Description

The consequences of failing to satisfy the written description requirement can be severe, and may include:

Loss of Priority: As an example, an inventor files a provisional application and then files a non-provisional application 12 months later with additional examples and data. If a relevant publication (e.g., an intervening art) emerges during that 12-month period, which describes one or more features of the invention described in the application and claimed, the publication may be applied as prior art. If the provisional application did not provide an adequate written description for the claims at issue, this could potentially render the invention obvious or anticipated, effectively destroying patentability.

Patent Invalidation: Even claims in issued patents can be invalidated for lack of a written description. If claims in a patent are challenged and the court finds that the claims lack adequate support in the specification, the claims may be declared invalid, rendering them unenforceable.

Best Practices for Meeting Written Description Requirements
While the legal landscape is complex, patent attorneys can take several approaches to strengthen the written description:

1. Provide Multiple Examples: When possible, include multiple representative examples spanning the scope of your claims.
2. Establish Structure-Function Relationships: Explicitly describe how structural features relate to functional properties.
3. Create "Blaze Marks": Provide clear pathways that demonstrate how a person skilled in the art would navigate from broad disclosures to specific examples.
4. Use Graduated Claim Scope: Draft claims with varying scope, from broad to narrow, to provide fallback positions if broader claims are rejected.
5. Thoroughly Describe Core Inventive Features: Ensure that the innovative aspects of your invention are described in detail.

Ultimately, the goal is to write an application that is not just good enough to get a filing date, but strong enough to survive prosecution and withstand future challenges.

Conclusion
A patent’s written description can be the deciding factor in determining whether you get allowable claims and whether claims in your patent are enforceable or even valid. Because the legal landscape is far from uniform, patent attorneys must carefully navigate the legal landscape and tailor their written description strategy to each invention. Court decisions consistently emphasize how fact-specific and nuanced this area is, making it clear that inventors and companies should treat the written description requirement as a strategic asset, not a checkbox.
If your patent matters, so does how it is written.

Questions about how to draft an effective written description for a patent? Pabst Patent Group specializes in intellectual property law in the biotech, pharmaceutical, and chemical industries and has helped numerous clients protect innovations. Our lawyers leverage their deep scientific, legal, and business expertise to create effective IP strategies to create real impact.
Contact us today to learn more.