It seems that Quine embarks on 4 different projects, believing that the completion of each is necessary for the other. I do not think so. The consequence of this structure is that the book feel quite disjointed, and many sections seem superfluous. In chapter 1, Quine introduces his behaviorist theory of language: linguistic items are conditioned responses to certain patterns of sensory stimulation. He proposes hypothetical principles of language acquisition that would make this theory possible. It amounts to an empirically unsupported outline of causal account of language (project #1); there is little 'philosophy' here.
Chapter 2 is the most rich and interesting chapter of the book. Here Quine argues for his influential theses of the indeterminacy of reference and the indeterminacy of meaning, which follow from his analysis of 'radical translation' (project #2). He presents a thought experiment in which a linguist tries to translate a totally alien language; her only data from which to construct a translation manual are observables, of the alien speaker's behaviors and environmental context. Quine argues that from this restricted set of data, the linguist can identify 'stimulus meanings' of the alien linguistic items. The stimulus meaning of a linguistic item is the conjunction of the set of stimuli, when paired with the linguistic item, provokes the speaker to indicate affirmation; and the negative set of stimuli, when paired, provokes the speaker to indicate dissent.
In order to construct a translation manual, the linguist would have to propose 'analytic hypotheses', which stipulate that an alien term and an English term share the same stimulus meaning. These hypotheses would serve as a foundation from which further translations could be inferred. Quine argues that it is possible for different linguists to end up with different translation manuals, which each equally account for the alien language, but which each are inconsistent with the other. This is because stimulus meanings are by nature referentially indeterminate (e.g., the stimuli of a rabbit could equally provoke the phrases "That's a rabbit!", "That's a particular instantiating rabbithood!", or "That's a collection of rabbit time-slices!"). Hence, reference is indeterminate, and so is meaning.
I think I need to read up more on Quine's argument because I see this flaw, which is too obvious to be a reasonable rebuttal: the conclusions of indeterminacy depend on the assumption that stimulus meaning exhausts the possible kinds of meaning that our linguistic items can have. This is obviously false. From our first-hand perspective, we can intend for our words to have very specific, determinate referents. Perhaps the indeterminacy of reference and meaning could be theoretically true regarding translation between languages, but it does not get us indeterminacy regarding the items of any given language itself -- it seems that Quine makes the latter, stronger claim. Maybe he doesn't though, and I've confused him as doing so because he refutes the traditional concepts of reference and meaning elsewhere (If anyone wants to help me out here, please do comment!).
In chapter 3, Quine presents an account of language acquisition in greater detail than in chapter 2 (continuation of project #1). I found this chapter superfluous and largely disconnected from the others; only some general points made here were relevant for the later chapters. In chapter 4, Quine examines how the references of certain types of linguistic items can be vague and ambiguous.
This seems like a prelude to chapter 5, in which Quine takes on his second project of "regimentation": to create a logical language that can simplify and consolidate the propositions of scientific theories (project #3). For him, this is crucial to expose the truth conditions of scientific propositions and to aid the progression of science. This is a very lengthy and tedious chapter; Quine goes through one type of syntactic structure and grammatical role after the other, evaluates competing philosophical treatments of their reduction into logical grammar, and promotes his own treatment. In only a few places does he rely on his causal account of language acquisition, to which he has dedicated previous chapters. Chapter 6 is a continuation of this project, with a particular focus on refuting the inclusion of intensional objects and propositional attitudes in logical grammar. In chapter 7, Quine switches to the task of defending a radical nominalism (project #4).
I would recommend potential readers to read chapter 1, patiently focus on chapter 2, and skim chapter 4. That is enough. Despite my disappointment with this book (which might be largely due to the intellectual-cultural difference of our time; Quine's naturalism does not seem radical from our modern eyes), I deeply appreciated some points, including his view of theoretical holism; his rejection of epistemological foundationalism; his attitude towards ordinary language; his criticism of conflating theoretical features with ontological features. I think if Quine took his own points more seriously, however, he would be more doubtful of, and even reject, the ontological and scientific claims that fill this book.