Substantial Similarity
The standard for proving copyright infringement by showing an accused work is similar enough to the protectable expression of the original that unlawful copying can be inferred.
Substantial similarity is one of the core elements a copyright plaintiff must prove, alongside ownership of a valid copyright and actual copying: that the accused work resembles the protected expression in the plaintiff's work closely enough to support a finding of infringement.
Courts use various tests to structure the comparison, including the extrinsic and intrinsic test in some circuits, and the abstraction-filtration-comparison approach commonly used for functional works like software, which filters out unprotectable ideas, facts, and standard elements (scenes-a-faire) before comparing what protectable expression remains.
In a simulation, similarity strength is best modeled as a continuous dial rather than a binary finding, feeding a probability estimate for the infringement branch that reflects how much of what was copied was actually protectable expression.
How it actually shows up
Experts and factfinders compare the works side by side, first filtering out elements the law does not protect, such as ideas, facts, and standard genre conventions, before assessing whether what remains is substantially similar. The analysis is a central battleground in software, music, and visual-art copyright disputes, where the line between protectable expression and unprotectable function or idea is often contested.
- Does substantial similarity require identical copying?
- No, it requires similarity in the protectable expression of the works, not word-for-word or pixel-for-pixel duplication.
- What is the abstraction-filtration-comparison test used for?
- It is used mainly in software copyright cases to strip out unprotectable functional elements before comparing what protectable expression remains between two programs.
- Does a plaintiff also have to prove access to the original work?
- Yes, typically a plaintiff shows the defendant had access to the copyrighted work alongside proving similarity, together supporting an inference of actual copying.
This page is an educational explainer, not legal advice, and creates no attorney–client relationship. Juricratic is a simulation engine: every probability-like figure is a dial you set, not a calibrated prediction. Verify every rule, deadline, and figure against the authorities and orders that govern your matter.
Turn the concept into a modeled matter.
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