The default rule in corporate law is that a company purchasing another company's assets buys the assets, not its liabilities -- the seller remains on the hook for its own debts, and the buyer starts clean. Successor liability is the set of recognized exceptions to that default, holding an asset purchaser liable for a predecessor's obligations when the transaction's structure or purpose makes treating the two companies as legally separate unfair to creditors, claimants, or the public.

The doctrine matters enormously in litigation because plaintiffs frequently find their original defendant judgment-proof, dissolved, or simply gone by the time a claim is litigated, and successor liability is often the only route to a solvent defendant. Because it can transform what looked like a clean asset sale into a liability-carrying acquisition, it is heavily litigated in product-liability, environmental, labor, and tax contexts.

Most jurisdictions recognize successor liability where: (1) the buyer expressly or impliedly agreed to assume the seller's liabilities; (2) the transaction amounts to a de facto merger -- continuity of ownership, management, personnel, physical location, and business operations such that the buyer is really a continuation of the seller in substance despite the asset-purchase form; (3) the buyer is a 'mere continuation' of the seller, typically shown by common ownership and control persisting across the transaction; or (4) the transaction was entered into fraudulently to escape liability to creditors.

The de facto merger and mere continuation exceptions overlap substantially and courts do not always distinguish them cleanly; both turn on substance-over-form analysis of whether the buyer is functionally the same enterprise as the seller, just wearing a new corporate name.

A significant minority of states, in the product-liability context specifically, have adopted a broader 'product line' exception, imposing successor liability where the buyer continues the seller's product line, benefits from the seller's goodwill and reputation for that product line, and the buyer's acquisition destroyed the injured plaintiff's remedy against the original manufacturer. This exception is notably more plaintiff-favorable than the traditional four exceptions and is not recognized in most jurisdictions.

Where it applies, the product-line exception can impose liability even absent any continuity of ownership or management, which makes jurisdiction selection especially consequential in mass-tort and product-liability litigation involving corporate successors.

Plaintiffs build the claim with evidence of the transaction's actual structure -- who retained ownership stakes, whether management and key employees carried over, whether the buyer held itself out as a continuation of the seller, and what consideration was paid relative to the assets' actual value (inadequate consideration is often evidence of a fraudulent transaction). In product-liability jurisdictions, plaintiffs also build the product-line continuity and destroyed-remedy showing.

Buyers attack by documenting an arm's-length transaction with fair consideration, distinct ownership and management before and after the sale, and an asset-purchase agreement that expressly disclaims assumption of the seller's liabilities. Because these exceptions are fact-intensive, successor liability disputes are frequently resolved on a developed record rather than at the pleading stage.

In Juricratic terms, successor liability starts from a strong default (no inherited liability) with each recognized exception modeled as a separate gate the plaintiff must open -- an assumption-language dial, a continuity-of-ownership-and-management dial for de facto merger and mere continuation, a fraudulent-purpose dial, and, in jurisdictions that recognize it, a product-line-continuity dial.

Because which exceptions are even available depends heavily on jurisdiction and industry, the model can be run under different jurisdictional assumptions to show how the same acquisition facts produce very different modeled exposure depending on whether the product-line exception is in play. These are simulation dials, not a claimed prediction of how a specific court characterizes the transaction.