What is the difference between a change in quantity demanded and demand?

Economists use similar terms for two things which are quite different: a change in the quantity demanded versus a change in demand. It can be a little confusing, so let's review. A change in quantity demanded refers to a movement along a fixed demand curve -- that's caused by a change in price.

What is a change in demand & supply?

Remember, when we talk about changes in demand or supply, we do not mean the same thing as changes in quantity demanded or quantity supplied. A change in demand refers to a shift in the entire demand curve, which is caused by a variety of factors (preferences, income, prices of substitutes and complements, expectations, population, etc.).

When does demand change?

Demand changes only when one of the determinants of demand change (recall the elements of the mnemonic TONIE). For instance, rising consumer incomes (one of the determinants) will increase demand for new cars, a normal good, which would shift the entire demand curve to the right. More cars will be demanded at every price when demand increases.