I read this book as a prolonged satire of the Principle of Sufficient Reason so beloved by the Western philosophical tradition. The principle states that there must be a rationally intelligible cause that suffices to explain any given phenomenon we might encounter. This principle is reflected in the Greek idea of Logos, which refers to the universal reason that inwardly structures all things, including human reason, which can know things only because it participate with them in universal reason. Logos is the pattern that maximally connects all things and that is also at work in the activity of the human mind, making possible knowledge of things. Much of the drama of Western philosophy is figuring out if the pattern that maximally connects things, and that in doing so, renders them intelligible for us, is "out there," discovered in things, or if it's "in here," constructed by our minds and projected onto things.
On the face of it, this cognitive need to encounter a thoroughgoing intelligibility in reality is as baked into humanity as is the need to procreate or excrete. Aristotle went so far as to argue that the human desire to know reality is even more fundamental, more essential to human nature, than the natural desires to feed and reproduce that we share with all other life forms. There is something to that view. When you're walking in the forest and hearing the rustling of leaves, your mind immediately leaps for the cause that ultimately makes sense of what you're hearing: is it a wolf, a deer, or just the wind? We are pattern-recognizing creatures. We live by bread only insofar as we first succeed in finding a pattern within which we, and the bread, intelligibly fit. But what justifies this fundamental principle? Why should we think that reality ought to make sense? What happens if we are forced, by our encounter with reality itself, to give up on our insistent, psychologically-comforting demand for thoroughgoing intelligibility?
Lem brilliantly depicts a limit situation in which the human animal's desire to optimize intelligibility breaks down. The human race encounters a signal sent by an alien intelligence so strangely framed, so radically Other, that it thwarts and repels any effort at assimilation within the human horizon of intelligibility. The refractory Other remains always inscrutable, always outside the luminous bubble of possible meaning secreted by the human animal, refusing assimilation into any conceptual scheme the humans studying it would impose upon it. Much of the dramatic impetus of this book arises from Lem's skillful depiction of the human mind's ever-renewed - and ever-repelled - attempt to assimilate the alien signal into a humanly meaningful pattern: a benevolent message from the gods, the Logos, the sufficient reason lurking behind things grown incarnate and speaking its secrets to us and justifying hope, etc.
IMHO, Lem's genius lies in exploring philosophical possibilities of the sci-fi genre that few others have managed to fully tap into. All quality sci-fi arguably tries to push the horizons of possible intelligibility just a little further. It tries to enjoin us to envision radically Other ways of making sense of things. In doing so, it exposes the blindspots of our usual taken-for-granted ways of interpreting things, interpretations that have become for us "just obvious" as we, through the force of habit, start to mistake them for the things themselves. Lem takes this feature of the genre to an extreme by considering the possibility of an Other, a Thou, in Buber's terms, that presents itself all right, but that does so as standing even further beyond the limit of our horizon of possible sense than does the human in relation to the dog's horizon of meaning.
He also presents and maps the possibility that the demands of intelligence for a total explanation that would reveal the purpose and value of things could come apart from life's visceral demands for the growth and preservation of structure. Over the course of the story, the scientists discover that the material substrate that carries the alien signal through space (which, in the story, turns out to consist of a configuration of neutrinos) has biophilic properties. That is, it contributes to the creation of conditions that support the growth of organic structure. The scientific community is led to a natural, human assumption: if the structure of the message is biophilic, it must be the product of good, benevolent senders. Such senders must love and affirm life and the cosmic order as good. However, Lem points out that a gap remains between the biophilic effect of the material structure of the message sent from the stars and the meaning of its informational layer. The latter remains inaccessible to us.
So, the human scientists could well capture the life-catalyzing, order-producing, structural features of the alien message, while utterly failing to penetrate into its semantic universe. We can see the structure without getting at the hidden sense. Nor can we get at the rational intention behind it. This is because we can only see reflected in the message the range of intentions we can find in ourselves. Every effort to bridge from structure to sense involves a projection of the sense the scientists themselves construct on the basis of their not-so-pure and all-too-human motives. And every effort to penetrate further into the horizon of meaning inhabited by this Other and to do so by stripping away every human projection of meaning is rewarded with failure.
Ultimately, Lem expertly shows us what it is like to attempt to push against the limits of the mind in the effort to make contact with and understand a genuine Other. The dramatic force of the tale stems from witnessing the dynamic of human collective intelligence, as embodied in the scientific process, as it stretches its tendrils to incorporate the signal into its inherited conceptual scheme, only to encounter pushback and recoil. With every failure to assimilate signal into meaning, the human animal is forced to recoil back upon itself as it only ever encounters a reflection of itself in each of its failed attempts to comprehend the Other. With each failed attempt to establish a meeting of minds, the human being only finds itself increasingly exposed in its egoism, greed, ignorance, aggression, and (possibly) irredeemable evil. And with each failed effort, we foreground the shape of the categorical filter that is both prison and inescapable home to our minds.
Lem leaves us with a stark possibility: that all that we have ever taken for "knowledge" and "discovery" of reality has really just been a more or less subtle form of anthropomorphic projection powered by our naked instinct for unchecked pattern-recognition. In other words, maybe reality doesn't respond to our desire for sense, after all. Maybe it will not play along and support our sense-making activities. Through it all, it remains intractably Other, and in it, we can only see ourselves. Maybe there is a sufficient reason in reality that makes sense of why the leaves rustled and explains the purpose of there being leaves at all with minds to know them. However, whatever that sense is that inheres in things themselves is not ours to enjoy, given what we have made ourselves to be.
So, Lem would reply to Aristotle that the desire for knowledge is itself propelled by far darker motives that lead us to a radical self-imprisonment. He seems to suggest that we are not capable of communing with reality and with others since we are never really open to conversing with anyone but ourselves. This being the case, if we don't manage to effect a radical transformation of the motives that viscerally propel us, including in our search for knowledge, we will only ever hit against the prisons of our own minds whenever we try to make contact with others and with the world around us.
I, for one, finished the book feeling a sad, inconsolable sense of claustrophobia. Thankfully, since I have limited capacities for reflection, it passed soon enough.