I hearing get who had but ears,
And sight, who had but eyes before;
I moments live, who lived but years,
And truth discern who had but learning's lore.
It is conceivable that Brooke had not read Thoreau, though not probable. What is probable is that he had read the lines and that their vivid comparison of physical and spiritual apprehension had taken seed in his fertile mind and germinated in due season.
It would not be easy for a man who wrote much to escape reminiscences of this sort. Even if he read nothing he would still inevitably hit on many ideas, similes, images, that others had used before him. The charge of plagiarism is only valid where the borrowing is deliberate and employed without creating new thought and new effects. Perhaps the most familiar illustration is that of Macaulay's New Zealander in the essay on Ranke's History of the Popes. It has been traced to many sources. It is found in Mrs. Barbauld and in Volney's Ruins of Empires. But the most exact parallel is this from Shelley's introduction to Peter Bell the Third:
Hoping that the immortality you have given to the Fudges you will receive from them; and in the firm expectation that when London is an habitation of bitterns; when St. Paul's and Westminster Abbey shall stand, shapeless and nameless ruins in the midst of an unpeopled marsh; when the piers of Waterloo Bridge shall become the nuclei of islets of reeds and osiers and cast the jagged shadows of their broken arches on the solitary stream; some transatlantic commentator, etc.
There is the whole vision complete, done in the spirit of comedy a generation before Macaulay dressed it in the pomp of his martial prose. Of course, Macaulay was familiar with the passage, and I assume he would have said that the idea was so exploited that it was common property which anybody was entitled to use who had a need and a use for it. And that is the best excuse that can be urged for most plagiarisms which are not mere cases of brazen theft or sheer desecration. It is the latter offence which is the more inexcusable. Honest stealing may be defended; but to steal and to degrade is past forgiveness. What adequate punishment could one devise for that queer ornament of the Church, Warburton, who in his Enquiry into the Causes of Prodigies and Miracles could, half a century after the publication of the Areopagitica, write thus:
Methinks I see her, like a mighty eagle, renewing her immortal youth and purging her opening sight at the unobstructed benign meridian Sun who some pretend to say had been dazzled and abused by an inglorious pestilential meteor; while the ill-affected birds of night would with their envious hootings prognosticate a length of darkness and decay.
If this banal nonsense is compared with Milton's original it will not be easy to deny it the distinction of being the most clumsy example of plagiarism on record. And Pope himself could not only plagiarise but belittle his plunder, as witness his appropriation of Jonson's fine lines:
What beckoning ghost, besprent with April dew,
Hails me so solemnly to yonder yew?
which he converts into:
What beckoning ghost along the moonlight shade
Invites my steps and points to yonder glade?