In a situation of decline in price of a Giffen Commodity, we find:

For a price fall, compensated substitution raises quantity demanded. A Giffen good is sufficiently inferior that the real-income gain lowers its demand by a larger amount, so total demand falls. Thus the positive substitution effect is smaller in magnitude than the negative income effect. The listed alternative describes an inferior but non-Giffen good; the last two reverse the quantity effects of a price fall.