Ética, Parte V, Proposición 12

Things, which we clearly and distinctly understand, are either the common properties of things or deductions therefrom (see definition of Reason, II. xl. note ii.), and are consequently (by the last Prop.) more often aroused in us. Wherefore it may more readily happen, that we should contemplate other things in conjunction with these than in conjunction with something else, and consequently (II. xviii.) that the images of the said things should be more often associated with the images of these than with the images of something else. Q.E.D.