It is necessary in the first place, that there be some impression immediately present to their memory or senses, in order to be the foundation of their judgment.

From the tone of voice the dog infers his masters anger, and foresees his own punishment.

From a certain sensation affecting his smell, he judges his game not to be far distant from him.
Secondly, The inference he draws from the present impression is built on experience, and on his observation of the conjunction of objects in past instances.

As you vary this experience, he varies his reasoning.

Make a beating follow upon one sign or motion for some time, and afterwards upon another; and he will successively draw different conclusions, according to his most recent experience.
Now let any philosopher make a trial, and endeavour to explain that act of the mind, which we call BELIEF, and give an account of the principles, from which it is derivd, independent of the influence of custom on the imagination, and let his hypothesis be equally applicable to beasts as to the human species; and after he has done this, I promise to embrace his opinion.