Levin had come across the magazine articles about which they were
disputing, and had read them, interested in them as a development
of the first principles of science, familiar to him as a natural
science student at the university. But he had never connected
these scientific deductions as to the origin of man as an animal,
as to reflex action, biology, and sociology, with those questions
as to the meaning of life and death to himself, which had of late
been more and more often in his mind.

As he listened to his brother's argument with the professor, he
noticed that they connected these scientific questions with those
spiritual problems, that at times they almost touched on the
latter; but every time they were close upon what seemed to him
the chief point, they promptly beat a hasty retreat, and plunged
again into a sea of subtle distinctions, reservations,
quotations, allusions, and appeals to authorities, and it was
with difficulty that he understood what they were talking about.

"I cannot admit it," said Sergey Ivanovitch, with his habitual
clearness, precision of expression, and elegance of phrase. "I
cannot in any case agree with Keiss that my whole conception of
the external world has been derived from perceptions. The most
fundamental idea, the idea of existence, has not been received by
me through sensation; indeed, there is no special sense-organ for
the transmission of such an idea."