A few general considerations on the subject may be offered:-- (a) Is the difference such as might be expected to arise at different times of life or under different circumstances ?--There would be nothing surprising in a writer, as he grew older, losing something of his own originality, and falling more and more under the spirit of his age.

'What a genius I had when I wrote that book!' was the pathetic exclamation of a famous English author, when in old age he chanced to take up one of his early works.

There would be nothing surprising again in his losing somewhat of his powers of expression, and becoming less capable of framing language into a harmonious whole.

There would also be a strong presumption that if the variation of style was uniform, it was attributable to some natural cause, and not to the arts of the imitator.
The inferiority might be the result of feebleness and of want of activity of mind.

But the natural weakness of a great author would commonly be different from the artificial weakness of an imitator; it would be continuous and uniform.