Todes's Body and World is first and foremost a study in epistemology. Much of the book can be loosely seen as dealing with the implications, consequences, and problems arising out of Kant's reformulation of the fundamental epistemological question.
Prior to Kant, that question was: (1) How do we come to know initially knowable objects? This question left open the possibility of there being more than one form of knowing since it was understood as the problem of “how we relate our perceptual kind of information about the object to our quite different conceptual kind of information about it.” (Todes, p. 92)
By positing that experience is a single synthesis of sensible intuition and conceptual understanding, Kant changed the problem to: (2) How do we make objects knowable? This form of the question makes the knowability of an object dependent on our [one] way of knowing (more on this transformation later) - in this case, through mentally subjective concepts (a.k.a. the information processing model of intelligibility, whereby concepts - and therefore, meanings - are superimposed onto raw sensible data). Hence, we are led to believe we can never know things-in-themselves.
Todes's treatment of the topic argues that question (2) is the result of an improper understanding of practical perception. One of his main theses is that Kant imaginizes perception - that is, Kant makes perception too mental.
In order to make sense of Todes's analysis, a background in Kant and phenomenology is invaluable. Husserl, Heidegger, and [especially] Merleau-Ponty are all important for getting the most out of Todes. For those looking to get a strong introduction into these subjects, here is a list of accessible readings:
Dreyfus, Hubert. 2005. "Overcoming the Myth of the Mental: How Philosophers Can Profit From the Phenomenology of Everyday Expertise." Proceedings and Addresses of the American Philosophical Association 79 (2): 47-65.
--Dreyfus lays out the philosophical landscape and explains why Todes's work is important.
Kelly, Sean. 2003. "Husserl and Phenomenology." The Blackwell Guide to Continental Philosophy. Solomon, Robert C. and David L. Sherman, Eds. Malden, MA: Blackwell, 112-142. Alternatively available at Kelly's page: http://www.people.fas.harvard.edu/~sdkelly/SDK-4-Publications.html
--Quite possibly the best [short] introduction to phenomenology.
Scruton, Roger. 2001. Kant: A Very Short Introduction. Oxford: Oxford University Press.
--An easy introduction to Kant. For more in-depth analyses, see Paul Guyer's Kant (Routledge, 2006).
Wrathall, Mark. 2012. "Heidegger on Human Understanding." (forthcoming in the Cambridge Companion to Heidegger's Being and Time) available at: http://www.markwrathall.org/papers/
--This is directed at those who have a background in Being and Time. Though Wrathall accepts "the pragmatist account of the vertical relationships between more and less deliberative acts, and between conceptually mediated and pre-conceptual acts," he argues that this type of story "fails to map on to Heidegger's account of understanding and interpretation" and that "Heidegger actually offers us... a horizontal account." In a way, this reading might bring Heidegger closer in line with Todes who claims that neither form of understanding (practical perception and conceptual imagination) is reducible to the other, though conceptual imagination nevertheless presupposes practical perception. It's all still an open issue for me.
My advice: Read Dreyfus (2005), then Kelly (2003) and (if you can) Wrathall (2012).
