In Chinese, the word “italics” or “italic” is translated 斜體 (xiétǐ / ce4tai2, “slanted type”). This is, in my personal opinion, one fine example of an accepted mistranslation that has stemmed from a gross misunderstanding of the subject matter. In the West, most — and I’d dare to say all — graphic designers would know that “slanted type” and “(true) italics” are very different animals.
Curiously, when I first got interested in typography, one of the books I read (that gave me a lot of insights) was The TeXbook, a software manual written by a professor of computer science (that is, neither a typographer nor a graphic designer) for a typesetting system he designed. Despite its ties to computer science — or perhaps due to the author’s in-depth research —, it knows to say
Slanted type is essentially the same as roman, but the letters are slightly skewed, while the letters in italic type are drawn in a different style. (p. 13) [My emphasis]
But what is this different style? In The Elements of Typographic Style, Robert Bringhurst elaborates on this in “Harmony and Counterpoint”:
It is true that most romans are upright and most italics slope to the right — but flow, not slope, is what really differentiates the two. Italics have a more cursive structure than romans, which is to say that italic is closer to longhand or continuous script. (p. 56) [My emphasis]
In my own words, what Dr. Donald Knuth and Robert Bringhurst are saying is that the italic form is essentially stylized calligraphy.
So we can now answer the question: Is there something in Chinese typography that corresponds to italics? The answer, in my opinion, is an obvious yes.
What we are looking for is something that is “drawn in a different style” than both serif (Song or Ming) and sans serif (gothic or Hei). We are looking for something that has a different “flow”, with a “cursive structure”, and “closer to longhand or continuous script” without being longhand or continuous script. We are looking for something that is in essence a form of stylized calligraphy.
There is an obvious candidate that fits all the above criteria: The “Kai” (楷) style.
With respect to how Chinese is treated in software a couple of things are now obvious. The first is of course that the use of slanted romans for “italics” is unnecessary. The second, which may not be obvious at first to some, is that the use of Kai type for “sans serif” (e.g., in Firefox, or in the GTK framework in Linux) is wrong.
There is a practical concern of whether Kai is suitable as a device for emphasis, and this is directly related to the fact that italic type has a different flow — in the case of Kai type, this different flow assumes a vertical writing direction. Kai, therefore, as a device for emphasis, would not exactly harmonize well with Latin italics in English copy. Despite this practical concern, however, one cannot deny that Kai is a form of italics and should be treated as such.