Upfront, I found it unclear who the book is aimed at. If this is an introductory book or for a popular audience (perhaps suggested by the appendix of basic terms at the end?), some of the terminology and ideas should be more carefully laid out and should reflect or acknowledge the consensus of the field. If this is a scholarly tome, some of the background literature should be more carefully acknowledged and debates discussed in detail.
For example, quite pertinent to my own interests, she quickly dismisses analogies between the structure of comics and the structure of language, stating that “…images communicate largely without rules… the smallest elements of images have no set meanings, and the way these elements are combined or even repeated are not governed by rules like grammar” (p. xvi). Viewpoints like this are repeated throughout the text, stated as accepted knowledge or as obvious, despite the absence of a scholarly consensus on the issue or any evidence to support it. (Compare this to Miodrag's recent Comics and Language—review coming soon—which spends 200+ pages discussing this argument!)
In fact, comparisons have been made along the lines she disparages since the 1970s within "semiotic" approaches to comics—the viewpoint she takes throughout (see my review "Comics, Linguistics, and Visual Language")—which go unreferenced. I assume her argument is directed against these researchers' theories, but it's hard to know without references or augmentation. My own work highlighting parallels between language and comics with a contemporary linguistics/cognitive viewpoint also go undiscussed and unreferenced throughout. It's hard to know whether such omissions are by choice (then: why?) or out of ignorance (which I doubt).
This again makes it unclear who the audience is: are readers supposed to take such flippant claims as reflecting the consensus of a field? Are they supposed to know that they reflect an opinion of a particular group of people (or at least, this author), but that there is an ongoing debate about this issue?
Clarity in this regard would aid the book on the whole, even if made as a note in the introduction, and would certainly aid me in reviewing it. I'd be more harsh on the book if it's meant as a scholarly treatise than if it's meant as an introductory book. I'll strike a middle ground here.
Theoretical contribution
This issue of audience permeates my main problems with the book, which is that I did not see much novelty in the theoretical contribution. Her broadest argument is that every level of structure in comics involves "filling in gaps" of information that go unprovided in their representations. This applies to the inferences about objects that are made by viewing only the simplistic forms of cartoony images as well as to the inferences created about a sequence by viewing only what is depicted in panels.
Certainly, no one denies that inference occurs in the understanding of sequences of images (or individual images), and indeed many people have said this, including McCloud, Saraceni, myself, and a host of others writing about comics (and other types of narratives!). Just how her theory of inference goes beyond others in any substantive way remains largely undiscussed. Is this a reflection of the book being aimed to an introductory audience? It's hard to tell.
A comparison may be useful: Saraceni's dissertation was extremely detailed, technical, and precise, only to be overly-simplified in the "textbook" version that was widely published as The Language of Comics (his articles fared better, striking a nice balance in tone). I haven't read Postema's dissertation, but such a simplification may be the case here as well.
In some ways, this book feels like a meshing of McCloud's focus on inference with a desire to simplify, clarify, and in some cases go beyond Groensteen's ideas, but aimed at a wider, less academic English-speaking audience (thankfully with less opacity than the original). For example, her contribution to discussing page layouts is merely to categorize the ways in which panels might be physically juxtaposed: do they have big gutters, no gutters, inset panels, etc? This focus on the physical is comparable to Groensteen's taxonomic treatment of how word balloons relate to panel borders (do they touch, do they overlap, etc). Such analyses at least provide a way to cut up the taxonomic space of comics, but they don't tell us much about their understanding. They're just a list of things in comics—and not even an all that interesting or insightful one!
Also, I certainly don't believe that all of these variations carry the intrinsic aspects of "meaning" that Postema seems to argue that juxtapositions in layout carry with them. For example, she makes much of the difference between when a single line separates panels versus having a larger gutter. However, when people first start drawing comics (for example, as kids and often adults), they usually just use single lines to separate panels. Do the "meaningful" "significations" of a gutter versus a line maintain in these, non-published works as well?
Semiotics vs. cognitivism
This example highlights the nature of a significant portion of my critique of the theory, no matter the audience. That is, the dissatisfaction with the book's orientation within a "semiotic" paradigm—a trend I'm finding in many recent works on comics and which I do not consider to be useful for looking at the formalist elements of this medium. These ideas draw from linguistics concepts from the 1930s until 1950s, principles of which were borrowed by the social sciences and humanities for looking at many other non-language domains. However, the actual study of language (i.e., linguistics and psychology) largely abandoned this approach in the 1960s in favor of ideas that attempt to describe principles of cognition, for which those "semiotic" ideas were not useful and only described a surface structure. Since that time, cognitive science research has developed enormously in ways that are insightful for describing language and beyond.
Though Postema appears to argue against a structuralist idea of language, she still maintains the broader framework of semiotics. There are many places where notions from contemporary linguistics or cognitive science would provide more convincing frames for the analyses of comics she makes (which, admittedly, are often insightful and interesting despite their non-cognitive framework). For example, Postema's discussion of Jacks Luck Runs Out by Jason Little nicely highlights how the story draws inspiration and structure from the rules and aesthetics of playing cards. However, her discussion remains at a surface level, stated in terms of connotation and denotation as if such principles carry with them explanatory power of "understanding."
In terms of cognitive science, this comparison would be covered by the theory of "conceptual blending," which illustrates how one domain of knowledge can creatively draw from another domain of knowledge. Blending theory would actually be beneficial for many of the examples discussed throughout. Granted, Postema's insights would likely remain much the same if framed in terms of blending, but framing them as such would allow her to probe deeper issues at work in this analysis, as well as to connect such a discussion of comics to how we understand the workings of the mind and brain more generally (and, dare I say it, language!).
As it stands, the analysis remains at surface level, without casting much light on what might be going on "under the hood" in the actual understanding of this material. This is especially true of the broader claim that readers "fill in gaps" when reading comics: Just what is creating this inference if not the mind/brain? And if it is the mind/brain (which I doubt Postema would deny), then why not actually target those principles guiding such processes?
Here is where the semiotic approach is most clearly lacking from cognitive approaches. It is important to remember that the "comic medium" itself does not actually contain these structures, as purported by the semiotic approach. Rather, the human brain is what instills and interprets such structures within the graphic form, so that is where our research should be focused in such matters.