When the cross price elasticity is positive, the two goods
are substitutes (e.g. Coca-Cola and Pepsi). In other words,
an increase in the price of one good will lead consumers
to shift demand towards the relatively cheaper substitute
good. When the cross price elasticity is negative the
goods are complementary goods (e.g. coffee and milk).
In other words, an increase in the price of one good will
negatively affect both its own demand and the demand of
goods that are usually bought to accompany it