Themistocles (I used to have a cat with that name)
If the non-working spouse does not have at least 40 qualifying quarters of work subject to SS tax, than her (I’ll assume for this it is a ‘her’, although this could be a ‘he’) benefit will be a spousal benefit, which will be a max of 50% of the working spouse’s PIA (the amount he’d get had he begun benefits in the month he attained his FRA) if she begins benefits in the month of her FRA. If she begins before this, the max 50% amount will be reduced by 25/32% per month up to 36 months begun early, and then 5/12% per month for months begun earlier than that. Note, the working spouse must begin benefits before the spouse is eligible for a spousal benefit (note: this is not true in a divorce where they were married at least 10 years).
Survivor benefits are a bit different and a bit too complicated to go into all possible situations here. Suffice to say, if the surviving spouse begins survivorship benefits prior to her FRA, they will be reduced just as they are in the above example. The one important actuarial difference is the survivorship benefits do not accrue delayed retirement credits (8%/yr) if the survivor waits to begin the survivorship benefit past her FRA.