Final answer:
The decline in middle-class family size after 1820 was due to factors like birth control use, financial considerations before marriage, and the desire to enhance living standards, not a shift towards families being viewed purely for functional usefulness.
Step-by-step explanation:
The decline in middle-class family size after 1820 is: 'a view of family more geared to functional usefulness than affection'. This does not explain the decline in birth rates or family size.Factors contributing to the decline in family size and birth rates in general include the use of birth control methods, delaying marriage until one had the financial means to support a family, and the parents' desire to improve the standard of living for themselves and their children.
Improved education, industrialization, urbanization, and economic shifts had significant impacts, leading to a demographic transition where families had fewer children. Birth control advancements, such as vulcanized rubber for contraceptives and educational pamphlets on family limitation, along with laws requiring children to attend school, thus contributing to declining birth rates as children became economic liabilities rather than assets.