To dread the shore which he sees spread with wrecks, is natural to the sailor.  I had before my eye, so many critical adventures ended in miscarriage, that caution was forced upon me.  I encountered in every page Wit struggling with its own sophistry, and Learning confused by the multiplicity of its views.  I was forced to censure those whom I admired, and could not but reflect, while I was dispossessing their emendations, how soon the same fate might happen to my own, and how many of the readings which I have corrected may be by some other editor defended and established.

  Criticks, I saw, that other’s names efface,
  And fix their own, with labour, in the place;
  Their own, like others, soon their place resign’d,
  Or disappear’d, and left the first behind,

  POPE.

That a conjectural critick should often be mistaken, cannot be wonderful, either to others or himself, if it be considered, that in his art there is no system, no principal and axiomatical truth that regulates subordinate positions.  His chance of errour is renewed at every attempt; an oblique view of the passage, a slight misapprehension of a phrase, a casual inattention to the parts connected, is sufficient to make him not only fails, but fail ridiculously; and when he succeeds best, he produces perhaps but one reading of many probable, and he that suggests another will always be able to dispute his claims.

It is an unhappy state, in which danger is hid under pleasure.  The allurements of emendation are scarcely resistible.  Conjecture has all the joy and all the pride of invention, and he that has once started a happy change, is too much delighted to consider what objections may rise against it.

Yet conjectural criticism has been of great use in the learned world; nor is it my intention to depreciate a study, that has exercised so many mighty minds, from the revival of learning to our own age, from the Bishop of Aleria to English Bentley.  The criticks on ancient authours have, in the exercise of their sagacity, many assistances, which the editor of Shakespeare is condemned to want.  They are employed upon grammatical and settled languages, whose construction contributes so much to perspicuity, that Homer has fewer passages unintelligible than Chaucer.  The words have not only a known regimen, but invariable quantities, which direct and confine the choice.  There are commonly more manuscripts than one; and they do not often conspire in the same mistakes.  Yet Scaliger could confess to Salmasius how little satisfaction his emendations gave him. Illudunt nobis conjectureae nostrae, quarum nos pudet, posteaquam in meliores codices incidimus.  And Lipsius could complain, that criticks were making faults, by trying to remove them, Ut olim vitiis, ita nunc remediis laboratur.  And indeed, where mere conjecture is to be used, the emendations of Scaliger and Lipsius, notwithstanding their wonderful sagacity and erudition, are often vague and disputable, like mine or Theobald’s.