8.  Among other opposite qualities of the mind, which may become dangerous, though in different degrees, I have often had occasion to consider the contrary effects of presumption and despondency; of steady confidence, which promises a victory without contest, and heartless pusilanimity, which shrinks back from the thought of great undertakings, confounds difficulty with impossibility, and considers all advancement towards any new attainment, as irreversibly prohibited.

9.  Presumption will be easily corrected.  Every experiment will teach caution, and miscarriages will hourly shew, that attempts are not always rewarded with success.  The most precipitate ardour will, in time, be taught the necessity of methodical gradation, and preparatory measures; and the most daring confidence be convinced, that neither merit nor abilities can command events.

10.  It is the advantage of vehemence and activity, that they are always hastening to their own reformation; because they incite us to try whether our expectations are well grounded; and therefore detect the deceits which they are apt to occasion.  But timidity is a disease of the mind more obstinate and fatal; for a man once persuaded, that any impediment is insuperable, has given it, with respect to himself, that strength and weight which it had not before.

11.  He can scarcely strive with vigour and perseverance, when he has no hope of gaining the victory; and since he will never try his strength, can never discover the unreasonableness of his fears.

12.  There is often to be found in men devoted to literature, a kind of intellectual cowardice, which whoever converses much among them, may observe frequently to depress the alacrity of enterprise, and by consequence to retard the improvement of science.

13.  They have annexed to every species of knowledge, some chimerical character of terror and inhibition, which they transmit, without much reflection, from one to another; they first fright themselves, and then propagate the panic to their scholars and acquaintances.

14.  One study is inconsistent with a lively imagination, another with a solid judgment; one is improper in the early parts of life, another requires so much time, that it is not to be attempted at an advanced age; one is dry and contracts the sentiments, another is diffuse and over-burdens the memory; one is insufferable to taste and delicacy, and another wears out life in the study of words, and is useless to a wise man, who desires only the knowledge of things.

15.  But of all the bugbears by which the infantes barbati, boys both young and old, have been hitherto frighted from digressing into new tracts of learning, none has been more mischievously efficacious than an opinion that every kind of knowledge requires a peculiar genius, or mental constitution, framed for the reception of some ideas and the exclusion of others; and that to him whose genius is not adapted to the study which he prosecutes, all labour shall be vain and fruitless; vain as an endeavour to mingle oil and water, or, in the language of chemistry, to amalgamate bodies of heterogeneous principles.