Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co. (2002)

Issues

• Does any narrowing amendment create an absolute bar to all equivalents for that limitation?
• If not, who bears the burden to show which equivalents remain?

Rules

• Presumption: A narrowing amendment for Patent Act compliance creates a presumption of prosecution history estoppel.
• No absolute bar: Estoppel does not automatically wipe out all equivalents.
• Burden: The patentee must show a specific equivalent was not surrendered.

Facts (Timeline)

Festo owned patents for a magnetic rodless cylinder used to move items in a system.

SMC released a similar device with a single sealing ring and a magnetizable alloy sleeve.

Festo alleged equivalents infringement; SMC argued prosecution history estoppel due to Festo’s amended claims (e.g., §112).

The district court found no estoppel; the Federal Circuit reversed, adopting an absolute bar rule.

Festo appealed to the Supreme Court.

Arguments

Judgment

The Supreme Court rejected the absolute bar. It held that a narrowing amendment creates a presumption of estoppel over the territory between the original and amended claims, but the patentee may rebut that presumption for particular equivalents.

• Focus is on how much coverage the amendment actually gave up.
• The patentee carries the burden to identify unsurrendered equivalents.

Ratio (Core Reason)

• Balance: Patents must give fair notice yet allow equitable protection.
• Presumption, not bar: Narrowing creates a presumption of estoppel, but leaves room for proof-based equivalents.
• Burden on patentee: They must show why a specific equivalent was not surrendered.

Why It Matters

Festo guides how courts read amended claims. It protects public notice while keeping the doctrine of equivalents alive. Innovators get clarity; patentees keep a fair chance to stop copycat tweaks.

Key Takeaways

• No absolute bar after narrowing amendments.
• There is a presumption of estoppel over surrendered ground.
• The patentee must prove which equivalents remain.

Mnemonic + 3-Step Hook

Mnemonic: “Narrow ≠ Never”

• Narrowing → creates a presumption.
• Not a never rule → no absolute bar.
• Need proof → patentee shows surviving equivalents.

3-Step Hook:

1. Ask: Was the amendment for Patent Act compliance?
2. Apply: Presume some equivalents were surrendered.
3. Assess: Did the patentee rebut with specific proof?

IRAC Outline

Issue: Do narrowing amendments create an absolute bar to equivalents?

Rule: Presumption of estoppel, but no absolute bar; patentee may rebut for specific equivalents.

Application: Amendment narrowed scope; court examined extent of surrender and allowed proof of surviving equivalents.

Conclusion: No absolute bar; remand to consider what, if anything, remains as an equivalent.

Glossary

Doctrine of Equivalents

Treats a slightly different device as infringing if it performs substantially the same function, way, and result.

Prosecution History Estoppel

Limits equivalents based on statements or amendments made to get the patent.

Narrowing Amendment

Changing a claim to meet Patent Act requirements, usually reducing scope.

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