The following comes from “Thomas Mann: Buddenbrooks” (Landmarks of world literature) by Hugh Ridley (Cambridge University Press, 1987).
Significance in general.
According to Ridley, critics don’t agree on the role of Schopenhauer’s philosophy in the novel.
Thomas Mann had been writing Buddenbrooks from 1897 to 1900. Mann said he'd read Schopenhauer’s book in 1899 and simply applied it to the episode he’s been writing at that moment:
the appropriateness of Schopenhauer to the novel stems from his
encounter with The World as Will and Imagination in the autumn of
1899, when, in an intoxication similar to Thomas's, he gulped down
this philosophy 'for days on end'. Mann's account of this episode
concludes with the claim that he incorporated his reading experience
into the manuscript of Buddenbrooks, 'which had just reached the point
at which Thomas Buddenbrook had to be brought to his death'
Some authors agree with this account, while others believe that Mann downplayed Schopenhauer’s role:
This 'instrumental' view of the role of Schopenhauer in the text is
taken up strongly by T. J. Reed (82). Frizen goes much further,
showing on the evidence of the Notebooks that Mann knew Schopenhauer
much more fully than Mann himself had claimed ([...] Vogt gives an account of this argument on p.80f);
while Erich Heller in a rightly celebrated chapter on Buddenbrooks
offers an interpretation of the entire novel in terms of
Schopenhauer's system. Expressing the central formula of the plot -
the decline of the will in the face of increasing reflective
consciousness, culminating in the total rejection of the will in
music, the art-form most removed from reality - Heller suggests that
the entire novel stands to Schopenhauer's philosophy as the Divina
Commedia does to Thomas Aquinas' theology: that the philosophy is
source and 'syntax' of the plot, that the novel is a brilliant
exegetic act on a canonical text.
Relevance of the episode.
The central argument of Schopenhauer's work is given in his title:
that the world can be experienced in two ways, as will and as
imagination. The world as will is that ceaseless struggle for
existence in which people spend their energies, asserting themselves
as individuals, striving and competing for illusory happiness and
success. It is this world as will of which Thomas (and his father
before him) sees in business life the partial reflection.
Schopenhauer believed that the real world is run by desire, blind and insatiable. However, in our everyday interactions, we don’t see the world as it is – what we see is only representation. Mann’s characters also start to see real life as arena for primitive instincts and forces under the veil of civility:
[Thomas] encountered there in business life something which he
understands as a feature of life itself, for business life is merely
'an image of the larger totality of life itself (8,4): the
falling-away of all pleasantness and conventionality as so much
play-acting 'in the face of the single raw, naked and domineering
instinct of self-preservation'. This experience has hurt him even more
than it had hurt his father. How often he has had to 'correct' his
personal emotions in order to try to diminish the hurt: how he has
wished to 'deal out harshness to suffer harshness, and to feel it not
as harshness but as something natural'. How often, in short, has his
hurt longing that life be different taken the form of pretending that
he is different, doing violence to his real nature, because he knows
that life cannot be changed. This is the conflict that has worn him
out.
This internal conflict brings suffering:
Another reason for Thomas's attraction to Schopenhauer is suffering:
Thomas's perennial experience, for which Schopenhauer gives a
theoretical foundation. In Schopenhauer's system, to live in the world
as will means to suffer. For the individual, suffering is part of the
very process of individuation, part of the self's creation of
particular needs and the unceasing effort to fulfill them - an effort
which is futile because the will knows neither rest nor fulfilment. It
is irrelevant which motives (firm, family, social status) lie behind
the striving which Schopenhauer shows by its very nature to lead to
suffering; motive is merely the form which the will has temporarily
adopted - 'what matters is that the will is exercised at all’ […]We
can understand the satisfaction with which Thomas realises that his
suffering has been brought into a system, and - so to speak –
justified.
Also a theme of death:
Thomas is suffering from the fear of death and the issue of personal
immortality that Schopenhauer so directly raises is anything but
academic to him. Schopenhauer met that painful insight which,
throughout his life, Thomas could only repress: that the goal to which
he was devoting his life and energy, his individual 'will', was
ultimately pointless.
Why does then Thomas end up affirming life?
Thomas ends his reading of a chapter, whose message is that it is good
to give up the individual will, by affirming not only life in general,
but that I behind it, the source of all individual willing and
suffering. Thomas must have misread Schopenhauer if he imagines that
it is an invitation to continue the dance of life.
Was there a scholar who understood Schopenhauer in such a peculiar manner?
German philosopher Friedrich Nietzsche replaced Schopenhauer’s concept of “will to life” by putting in the center a notion of “will to power” (thereby influencing subsequent generations of 20th century thinkers). From Schopenhauer: A Very Short Introduction by Christopher Janaway:
Plumbing the depths of the Schopenhauerian vision is a necessary step,
but there must be an alternative to the ‘life-denying’ attitude of
seeking to escape from the will and despising the individual material
being that one is. Nietzsche’s proposed solution is that of a creative
self-affirmation (‘Become who you are!’), embracing one’s pain and
even one’s cruelty as true parts of oneself.
Ridley continues:
This is not Schopenhauer at all - although it is a half quotation from
him - the source of this affirmation of life is recognisably
Nietzsche, and Thomas has invoked a scaled down version of the blond
beast, the one who says ‘I’.
So Ridley thinks this reflects both Thomas’ inability to stand outside life and Mann’s influences outside the text.
Contemporary audience.
Can we expect the 1901 audience to recognise the book? This depends on what audience we have in mind.
According to Ridley the novel was read mostly by educated public:
If Buddenbrooks has achieved, in the course of this century, a
readership that is both popular and specialised, this cannot disguise
the fact that in its day the novel was liable to be understood only by
the specialist group.
It seems these educated readers would be able to recognise the book.
Mann gives the title of the chapter Thomas reads ('On Death and its relation to the indestructibility of our true nature'), and Thomas sees himself as “Organism! Blind, thoughtless, pitiful eruption of the urging will!” It’s hard to see whose work this could’ve been confused with.
Schopenhauer was extremely popular in the second half of the 19th – early 20th century. From VSI book:
In fact, not to have read Schopenhauer would have been the odd thing
for a young person from a cultured family such as Wittgenstein’s.
However, this is probably not the audience Mann hoped to attract:
he was still far from having a realistic view of his public. This
emerged in his understandable, but rather naive, request to his friend
Otto Grautoff to review the novel in such a way as to assure for it a
good reception among readers in Lübeck.
The split between the actual reading public for quality literature and
the public Mann seemed to aim at (the traditional middle classes about
whom he wrote) was a well-known feature of the German literary scene.
As one reviewer of Buddenbrooks commented: it was irrelevant to the
German public if a novel is written well or badly' (Eloesser, 1281) -
such matters were for the specialised readers of literature.
How likely is that this desired audience’s read Schopenhauer? Ridley says that it would not be unusual for someone like Thomas Buddenbrook to encounter The World as Will and Representation:
Thomas's acquaintance with Schopenhauer is anything but accidental
(indeed, Schopenhauer's popularity at the end of the nineteenth
century makes it a typical experience)
I take it as there being some non-zero chance that a member of the bourgeoisie would've read the book. This might also suggest that for Mann it wasn’t that important that his readers understood what book Thomas was reading.