56. Shifts in the supply and demand curves

Shifts in supply and demand curves are caused by all the things other than price. So a shift to the right of a supply curve (or a shift up - same thing) is as a result of more suppliers that have entered the market (if you have understood that the marginal cost curve represents the supply curve this post is redundant) a shift to the right of a demand curve (or a shift up - same thing) is as a result of more customers that have entered the market - this is as a result of a demographic increase or that the disposable income of a particular group of customers have increased.

So a shift to the left of a supply curve is as a result of ... just the opposite of what was said in the previous paragraph.

If this does not make too much sense to you, you may want to start here.