Arthur's Doubt

I am going a long way
With these thou seëst—if indeed I go	65
(For all my mind is clouded with a doubt)—
To the island-valley of Avilion;
Where falls not hail, or rain, or any snow,
Nor ever wind blows loudly; but it lies
Deep-meadow’d, happy, fair with orchard lawns	70
And bowery hollows crown’d with summer sea,
Where I will heal me of my grievous wound.”

-copied from here.

Curious about what had been left out of the Tennyson quotation here, I found that it was Arthur's doubt. Shakespeare also incorporates doubt:

So have I heard and do in part believe it.
-copied from here.

Such doubt signals the transition to the modern period expressed by contemporary novels and sf.