Even though manga has lots of different art styles we still have an idea that certain styles are "manga style" and other ones aren't. What is it about an art style that lets us know it's manga style? What elements reappear across many manga? What distinguishes our idea of manga style from our idea of Western comics style?
I'm not sure there is a specific answer to this. As you acknowledge, different artists have different styles. Both Japanese and western books vary from "cartoony" to "realistic". There are cultural differences seen in the art, such as in Japanese media adults often smoke, while in American media, they seldom do -- definitely not in titles geared to children. (Maybe they do in French media; that's why I switched from "western" to "American".)
Hell, sometimes an artist has extremes in his own work; consider Yoshiro Togashi and his "bad days" on Hunter x Hunter. Here is a comparison of a page that got published in the weekly mag, versus how he improved it for the HxH volume:
Is the left even identifiable as manga vs comic book (vs fan art)? On the right, the main clue as to being a manga, at least to me, is the eyes of the upper right character. Otherwise it could be from a (somewhat dark) American funny-animal comic book, a la "Fritz the Cat visits a jungle".
Let's look at another page:
Is there anything innately Japanese or western concerning Jack Katz' work on The First Kingdom? If I didn't already know, I could not tell anything except that he is a remarkable artist (a mangaka in every sense of the word except his nationality). ... Hmm, maybe in Japan they would have to fade-out all the nipples.
I myself instantly recognize manga because the pages have to be read from right to left. The other instantly recognizable hint is that manga are typically b&w, whereas western comics are usually color.
I could be wrong, but based on observation, here is a theory:
"Manga-style" refers to the shading process. Compare the conversions from books to animation, there is much less line shading due to grayscale limitations not applying to animation, especially with coloring.
Furthermore, just the facial style of western cartoons, in comparison to Japan in specific, eases the differences.
well to me It's more about the lack of details. Be-sided the obvious eyes (tough they come in different styles) the main deference to me between comics and manga it's the lack of realism. Comics use a lot of details in the hair, eyes, shading, and body...making the characters look more realistic. But in Manga for example they gather a bunch of hair into two line strokes and gives volume with shading, a vary cleaner look to the character. Idk, just less realistic I suppose.
If you do research you will find that the Japanese consider animation such as cartoons and anime to all be anime but some styles are usually seen separately.
The main difference is the age. What we call cartoons are things aimed at kids, while anime is usually aimed at older people as well as young but the so called cartoons pokemon and yugioh are anime.
The thing is us Americans just separated everything.
a style of animation originating in Japan that is characterized by stark colorful graphics depicting vibrant characters in action-filled plots often with fantastic or futuristic themes.
a simple drawing showing the features of its subjects in a humorously exaggerated way, especially a satirical one in a newspaper or magazine. synonyms: caricature, parody, lampoon, satire; More
a motion picture using animation techniques to photograph a sequence of drawings rather than real people or objects.
if it helps most of the cartoons we have in america are made in japan.and all of this started in japan.