By theory, I mean mostly how the Chinese culturally think about food.
He gives five terms that reflect primal values of chinese cuisine, Hsien--sweet natural flavor, Hsiang-characteristic fragrance, Nung-rich, heady, concentrated; yu-er-pu-ni-to taste of fat without being oily such as properly cooked pork belly.
His very first recipes focus on the plain flavors of food, the base essence. Boiled rice, poached chicken and so on. Establish as a baseline the characteristics of the ingredients and those dishes that do that.
Then, he starts to move into the flavors more. Carp in Lamb Broth as an early in the discussion of complementary flavors as an example. The introduction to this recipe:
We elucidate the common principle by exaggeration. The flavour of lamb is very sweet, though rank. The rankness is suppressed by cooking with wine. Carp is the richest and meatiest of all fish, and requires the support of a meat broth. The fish and lamb broth are eaten together, with a spoon. Each tastes of itself, but at the point where they meet, there is no difference. The effect is very complex, novel and amusing. The emasculated delicacy of this recipe is typical of Soochow gastronomy discussed at length in Chapter 4. The word Hsien (sweet and the character for it) is composed of the fish and the lamb. They have met.
And check out this chart. It runs a couple of pages in the book but here's a section (click the image to read it in a larger format:
He's explaining why ingredients and techniques are used and what they are thought to accomplish as well as linking a sample recipe. So theory of the cuisine. It's this sort of understanding of a cuisine and the related technique that free you from recipes. You can look in your fridge and intuit what to do with what you have available. His explanation of the uses of ginger for example really opened my mind to the ingredient. I had simply viewed it as adding the ginger flavor to the dish. But no. It's more often used to correct a perceived flaw in the flavor. To remove fishiness in fish, the sulfurous rankness of meat, the grassiness of green vegetables. You'll often not taste the ginger at all or it might be cooked in the oil, then removed. Of course, there are times it is used for it's own flavor as well.