Philosophers Vardy and Grosch use the example of a fruitcake to show how all 4 parts of the brain can be used for making decisions. The vegetative part recognises that I am hungry, it tells me to eat. The desiderative part may desire cake to satisfy the hunger: something I want, but not necessarily need. The scientific part of the soul knows that fruit is better for me than cake and the calculative part, weighing up the evidence, comes up with the suggestion of fruitcake. Thus using all parts of the soul.