In this section Hicks summarizes the conclusions thus far about the law of demand. The demand curve (expressing the quantity of a commodity demanded as a function of its price) must always slope downward whenever the commodity is not an inferior good. Even when the commodity is an inferior good, the demand curve will still slope downward as long as the proportion of income spent on the commodity is small. And finally, even if neither of the above qualifications apply, the demand curve may still slope downward if substitution effects are large.
Hicks notes that, "Consumers are only likely to spend a large proportion of their incomes on what is for them an inferior good if their standard of living is very low," and he notes that the Giffen case, quoted by Alfred Marshall exactly fits this description. But cases such as this are clearly rare.
Therefore, Hicks concludes that, "The simple law of demand -- the downward slope of the demand curve -- turns out to be almost infallible in its working. Exceptions to it are rare and unimportant."
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