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And now that we have surrounded the intellect with faithful helps and guards, and got together with most careful selection a regular army of divine works, it may seem that we have no more to do but to proceed to philosophy itself.  And yet in a matter so difficult and doubtful there are still some things which it seems necessary to premise, partly for convenience of explanation, partly for present use.

Of these the first is to set forth examples of inquiry and invention according to my method, exhibited by anticipation in some particular subjects; choosing such subjects as are at once the most noble in themselves among those under inquiry, and most different one from another; that there may be an example in every kind.  I do not speak of those examples which are joined to the several precepts and rules by way of illustration (for of these I have given plenty in the second part of the work); but I mean actual types and models, by which the entire process of the mind and the whole fabric and order of invention from the beginning to the end, in certain subjects, and those various and remarkable, should be set as it were before the eyes.  For I remember that in the mathematics it is easy to follow the demonstration when you have a machine beside you; whereas without that help all appears involved and more subtle than it really is.  To examples of this kind,—­being in fact nothing more than an application of the second part in detail and at large,—­the fourth part of the work is devoted.

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The fifth part is for temporary use only, pending the completion of the rest; like interest payable from time to time until the principal be forthcoming.  For I do not make so blindly for the end of my journey, as to neglect anything useful that may turn up by the way.  And therefore I include in this fifth part such things as I have myself discovered, proved, or added,—­not however according to the true rules and methods of interpretation, but by the ordinary use of the understanding in inquiring and discovering.  For besides that I hope my speculations may in virtue of my continual conversancy with nature have a value beyond the pretensions of my wit, they will serve in the meantime for wayside inns in which the mind may rest and refresh itself on its journey to more certain conclusions.  Nevertheless I wish it to be understood in the meantime that they are conclusions by which (as not being discovered and proved by the true form of interpretation) I do not at all mean to bind myself.  Nor need any one be alarmed at such suspension of judgment, in one who maintains not simply that nothing can be known, but only that nothing can be known except in a certain course and way; and yet establishes provisionally certain degrees of assurance, for use and relief until the mind shall arrive at a knowledge of causes in which it can rest.  For even those schools of philosophy which held the absolute impossibility of knowing anything were not inferior to those which took upon them to pronounce.  But then they did not provide helps for the sense and understanding, as I have done, but simply took away all their authority:  which is quite a different thing—­almost the reverse.