In a typical mortgage loan, what is the role of the promissory note versus the mortgage (or deed of trust)?

A financed purchase involves two key instruments. The promissory note is the borrower's written promise to repay the loan — it states the amount, interest rate, payment terms, and is the evidence of the debt. The mortgage (or, in many states, a deed of trust) is the security instrument: it pledges the real property as collateral and gives the lender the right to foreclose if the borrower defaults. The note creates the personal obligation; the mortgage attaches that obligation to the property. In deed-of-trust states a third party (the trustee) holds title until the loan is repaid. Distinguishing the debt instrument from the security instrument is core financing content.