What is the relationship between consumption and disposable income?
Consumption function _is_ the relationship between consumption and disposable income, namely it’s a function that gives you the consumption amount given any disposable income. Same for savings function. Consumptions should add up to disposable income. Consumption cannot be negative, but savings can be, if we allow for borrowing or have an open economy. If savings are can be negative, consumptions can exceed disposable income. Finally, it is commonly assumed that consumption is an increasing function of disposable income.
