What else affects demand? Lots of things: Income; tastes; price of substitutes; price of complements (goods that you consume together, such as caffeine and computers); and expectations, to name a few. There are others too: changes in age or income distribution in the population, changes in population size. You can probably think of even more. But, if only price changes, we can reasonably expect the desired quantity demanded to decrease as the price increases, and vice versa. This gives rise to the inverse relationship between the price and the desired quantity demanded, or the law of demand.