This article is from the Tolkien FAQ, by William D.B. Loos loos@hudce.harvard.edu with numerous contributions by others.
Yes. Originally, the world of the Hobbit was not the same as the world
of the Silmarillion (Tolkien threw in a few names from it, like Gondolin and
Elrond, for effect, but there was no explicit connection). Thus, when he
began LotR, he thought he was writing a sequel to _The Hobbit, and the tone
of the early chapters, especially Ch 1, reflect this (it has the same
"children's story" ambience as _The Hobbit_). With the coming of the Black
Riders and Gandalf's discussion of Middle-earth history and the Ring a change
began towards a loftier tone and a darker mood, though much less serious
elements remained (e.g. Tom Bombadil). After the Council of Elrond LotR
was overtly a sequel to the Silmarillion.
Oddly, Tolkien added new details but never changed the overall tone of
Book I. He later claimed that the change in tone was intentional, that it
was meant to reflect the changing perceptions of the hobbits as they became
educated about the Wide World. This was certainly not his intention as he
was writing. On the other hand, the tone of "The Scouring of the Shire" is
very different from that of "A Long-expected Party", possibly indicating the
altered perspective of the observers.
 
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