A buyer acquires property using the existing mortgage where the original owner remains responsible for the debt. This process is known as:

In this scenario, when a buyer acquires property using the existing mortgage while the original owner remains responsible for the debt, the process is indeed known as assumption. This term refers to the buyer taking over the mortgage payments from the seller, effectively "assuming" the financial obligation tied to the mortgage. The seller's name remains on the mortgage, which means that they still hold liability for the debt in addition to the buyer's new responsibility.

In contrast, novation would involve the original debt being replaced with a new obligation, thereby releasing the original owner from liability, which is not applicable in this case. Transfer of title simply refers to the legal process of changing ownership of the property but does not inherently involve the assumption of a mortgage. Substitution refers to replacing one thing with another, which is not relevant in the context of mortgage responsibility and property acquisition.