The excerpt provided seems to discuss the uncertainty and ever-changing nature of literature, philosophy, and aesthetics. It suggests that predicting what ideas and modes of expression will prevail or perish is a challenging task, highlighting the constant evolution and unpredictability of creative fields. The mention of hope at the end of the excerpt may signify a belief in the enduring power of innovation and creativity despite the unknown future.
In terms of the source of the quote, without a specific author or work mentioned in the question, it is challenging to attribute it accurately. However, such themes of unpredictability and the evolution of ideas are common in various literary and philosophical works. One possible source where similar ideas may be explored could be works by postmodernist authors or thinkers who often delve into the complexities of language, interpretation, and the fluidity of meaning.
Therefore, the excerpt's sentiment resonates with a broader discussion on the nature of creativity, change, and the intrinsic uncertainties present in artistic and intellectual endeavors.