# What is the economic intuition behind cross derivatives?

Suppose I have a utility function $$u(c,l)$$, where c is consumption and l is leisure. What does $$u_{cl}$$ mean in economic terms for example, or in general what is the economic meaning of cross derivatives?

Generally cross-derivative $$f_{xy}’’$$ tells you how the slope $$x$$ changes with respect to changes in $$y$$.
When it comes to the utility $$u(c,l)$$ the cross derivative $$u_{cl}’’$$ tells you how much the marginal utility of $$c$$ changes when you change amount of $$l$$.