I. When we are enquiring into the causes of any particular effect or appearance, either in the world of nature, or in the civil or moral concerns of men, we may follow this method :

1. Consider what effects or appearances you have known of a kindred nature, and what have been the certain and real causes of them; for like effects have generally like causes, especially when they are found in the same sort of subjects.

2. Consider what are the several possible causes which may produce such an effect: and find out by some circumstances how many of those possible causes are excluded in this particular case: Thence proceed by degrees to the probable causes, till a more close attention and inspection shall exclude some of them also, and lead you gradually to the real and certain cause.

3. Consider what things preceded such an event or appearance, which might have any influence upon it; and though we cannot certainly determine the cause of any thing only from its going before the effect, yet among the many forerunners we may probably light upon the true cause by further and more particular enquiry.

4. Consider whether one cause be sufficient to produce the effect, or whether it does not require a concurrence of several causes; and then endeavour as far as possible to adjust the degrees of influence that each cause might have in producing the effect, and the proper agency and influence of each of them therein.

So in natural philosophy, if I would find what are principles or causes of that sensation which we call heat when I stand near the fire; here I shall find it is necessary that there be an agency of the particles of fire on my flesh, either mediately by themselves, or at least by the intermediate air; there must be a particular sort of motion and vellication imprest upon my nerves; there must be a derivation of that motion to the brain: and there

must be an attention of my soul to this motion: if either of these are wanting, the sensation of heat will not be produced.

So in the moral world, if I enquire into the revolution of a state or kingdom, perhaps I find it brought about by the tyranny or folly of a prince, or by the disaffection of his own subjects; and this disaffection and opposition may arise either upon the account of impositions in religion, or injuries relating to their civil rights; or the revolution may be effected by the invasion of a foreign army, or by the opposition of some person at home or abroad that lays claim to the government, &c. or a hero who would guard the liberties of the people; or by many of these concurring together; then we must adjust the influences of each as wisely as we can, and not ascribe the whole event to one of them alone.

11. When we are enquiring into the effects of any particular cause or causes, we may follow this method:

1. Consider diligently the nature of every cause apart, and observe what effect every part or property of it will tend to produce.

2. Consider the causes united together in their several natures, and ways of operation: enquire how far the powers or properties of one will hinder or promote the effects of the other, and wisely ba lance the propositions of their influence.

3. Consider what the subject is, in or upon which the cause is to operate: for the same cause on different subjects will oftentimes produce different effects; as the sun which softens wax will harden clay.

4. Be frequent and diligent in making all proper experiments, in setting such causes at work, whose effects you desire to know, and putting together in an orderly manner such things as are most likely to produce some useful effects, according to the best survey you can take of all the coneurring causes and circumstances.

5. Observe carefully all the events which happen either by an occasional concurrence of various causes, or by the industrious applications of knowing men and when you see any happy effect certainly produced, and often repeated, treasure it up, together with the known causes of it, amongst your improvements.

6. Take a just survey of all the circumstances which attend the operation of any cause or causes, whereby any special effect is produced: and find out as far as possible how far any of those circumstances had a tendency either to obstruct or promote, or change those operations, and consequently how far the effect might be influenced by them.

In this manner physicians practise and improve their skill. They consider the various known effects of particular herbs or drugs, they meditate what will be the effects of their composition, and whether the virtues of the one will exalt or diminish the force of the other, or correct any of its nocent qualities. Then they observe the native constitution, and the present temper or circumstances of the patient, and what is likely to be the effect of such a medicine, on such a patient. And in all uncommon cases they make wise and cautious experiments, and nicely ob serve the effects of particular compound medicines on different constitutions and in different diseases, and by these treasures of just observations they grow up to an honourable degree of skill in the art of heal ing. So the preacher considers the doctrines and reasons, the precepts, the promises and threatenings of the word of God, and what are the natural effects of them upon the mind; he considers what is the natural tendency of such a virtue or such a vice; he is well apprized that the representation of some of these things may convince the understanding, some may terrify the conscience, some may allure the slothful, and some encourage the desponding mind; he observes the temper of his hearers, or of any particular person that converses with him

about things sacred, and he judges what will be the effects of each representation on such persons; he reviews and recollects what have been the effects of some special parts and methods of his ministry; and by a careful survey of all these he attains greater degrees of skill in his sacred employment.

Note, In all these cases we must distinguish those causes and effects which are naturally and necessarily connected with each other, from those which have only an accidental or contingent connexion. Even in those causes where the effect is but contingent, we may sometimes arrive at a very high degree of probability; yet we cannot arrive at such certainty as where the causes operate by an evident and na tural necessity and the effects necessarily follow the operation. See more on this subject, Logic, Part II. Chap. V. Sect. 7.

CHAP. XX.

of the Sciences, and their Use in particular Professions.

I. THE best way to learn any science, is to begin with a regular system, or a short and plain scheme of that science, well drawn up into a narrow compass, omitting the deeper and more abstruse parts of it, and that also under the conduct and instruc tion of some skilful teacher. Systems are necessary to give an entire and comprehensive view of the several parts of any science, which may have a mu tual influence toward the explication or proof of each other whereas if a man deals always and only in essays and discourses on particular parts of a science, he will never obtain a distinct and just idea

of the whole, and may perhaps omit some important part of it, after seven years reading of such occasional discourses.

For this reason young students should apply themselves to their systems much more than pamphlets. That man is never so fit to judge of particular subjects relating to any science, who has never taken a survey of the whole.

It is the remark of an ingenious writer, should a barbarous Indian, who had never seen a palace or a ship, view their separate and disjointed parts, and observe the pillars, doors, windows, cornices and turrets of the one, or the prow and stern, the ribs and masts, the ropes and shrouds, the sails and tackle of the other, he would be able to form but a very lame and dark idea of either of those excellent and useful inventions. In like manner, those who contemplate only the fragments or pieces broken off from any science, dispersed in short unconnected discourses, and do not discern their relation to each other, and how they may be adapted, and by their union procure the delightful symmetry of a regular scheme, can never survey an entire body of truth, but must always view it as deformed and dismembered; while their ideas, which must be ever indistinct and often repugnant, will lie in the brain unsorted, and thrown together without order or coherence: such is the knowledge of those men who live upon the scraps of the sciences.

A youth of genius and lively imagination, of an active and forward spirit, may form within himself some alluring scenes and pleasing schemes in the beginning of a science, which are utterly inconsistent with some of the necessary and substantial parts of it which appear in the middle or the end. And if he never read and pass through the whole, he takes up and is satisfied with his own hasty pleasing schemes, and treasures these errors up amongst his solid acquisitions; whereas his own labour and study far