When a student first begins the study of Shodo, it is common for them to begin to experiment with brushing the various other styles (“beyond” the initial one of Kaisho, or “block-script”). There's nothing wrong, or even detrimental to doing so, they are simply expanding their “skill base”. The thing which should be avoided though, is assuming that one is performing these styles correctly. As long as one is “copying” a known (to be correct) “model”, or “Tehon”, then the student can be assured that they are practicing the correct motions/strokes. Where many students go astray, is when they begin to make assumptions about how every kanji is done in those styles which are unfamiliar to them.
To follow the “path” of Shodo, one assumes the responsibility of following the recognized “guidelines” of a character's creation (“brushing”). There are specific guidelines and rules that required (to be considered “correct”) when performed. Simply using a brush” to write Chinese/Japanese character's, does not mean one is a practitioner of “Shodo” . One can use a pencil to write Kanji, this also doesn't equate to practicing “Shodo”.
The practice of Kaisho, can often be disregarded, by “believing” that it is (considered) to be “Basic”. Kaisho (IMO) can be one of the most frustrating styles to brush (correctly). This mainly is a result of more people who can easily recognize when mistakes are made. By venturing into the “other” methods/styles, the amount of “critique” will become (more) limited (thus reinforcing the individual's “self-belief” of doing the style “correctly”).
Often students who have either gone without (or have simply abandoned) their instructor's guidance, make poor decisions (a.k.a. “assumptions”) about what is considered the correct method of brushing these different styles. Gyosho, is what is commonly associated with being the manner which is usually brushed (in “everyday” writing). It's more relaxed, and all of the same rules for the Kaisho style can still (albeit “loosely”) followed without making any major “flaws” or mistakes. There are certain accepted “short-cuts” and stroke eliminations, that are well known and recognized. This does not equate to allowing the individual to “create” their own “short-cuts” and stroke changes. These would simply be viewed as amateurish attempts at (self-believed) “creativity”. In personal correspondence, these mistakes would no-doubt be over looked/ignored, but if one is planning on “displaying” those pieces, they would only point out the individual's lack of knowledge (and certainly not “skill”).
These same student's (who abandon their training) often turn to “Zen” (style?) Calligraphy. Zen Calligraphy is a more “open” style, and tends to abandon the recognized “rules”(or at least operates outside of them, usually to provide a visual “lesson” from the manner it was brushed). This can amount to an “excessive” use of ink (in effect, “blotting”) which creates a “bleeding” of ink into the paper, or using the “side” of the brush to write with (while not expanding the size of the area utilized for the character, which gives a “blurred” effect). Regardless of the effect attempted, the character remains “legible”. This “style” is rather “individual” in nature, often displaying the artist's own personality and/or “message” that is being displayed by the piece's exhibition. What is “more often” displayed from these attempts, is the artist's own “scattered” thoughts, and lack of (ability to) “focus”.
I've noticed that person's attempting the “Sosho”(fully-cursive”) style of brushwork, tend to be (and is very popular) among the various “American” martial arts schools. This style of brushwork, has a very “defined” set of rules to it's execution. The strokes must be done in a very precise manner, and order, for the character to not be confused with other “similar” kanji. Sosho gives the “illusion” of being “hastily” brushed, very often this style of brushwork is done slowly, and precisely. It's this “illusion”, that causes many student's to falter at achieving the correct appearance. Because it is so little known (as to the correct manner of it's execution) by much of the native Japanese (much less “American's”) population,, it's commonly “assumed” to be just a quickly brushed “Gyosho” (which is far from being accurate). Sosho utilizes strokes, and stroke order from older scripts (from before even Kaisho's inception). Though Kaisho, and Gyosho share many common strokes, Sosho has different “roots”, so the comparison (to them) is often unjustified. It is virtually a separate language unto itself (which may account for over 85% of the Japanese population not being even able to even read it, much less “correctly” brush it).
Regardless of the style utilized, the same guides for “correctness”, should always apply:
Itten shuchu “Perfect concentration”
Aside from the shodoka's (own)“focus” upon the piece, the same should be provided by the piece being brushed (by not “scattering” the observer's ' “vision” as they view the workpiece.
Ichi ji keizoku “One action continued”
Though (also) meaning to “focus” upon the task at hand (meaning the shodoka), the observer's vision should “follow” the strokes of the piece.
Kansho shimbi “Appreciation of beauty”
While including the “correct” manner of brushing the character's, this should include the “synchronicity” of the whole piece. If the work does not “flow” together, the viewer's (attention?) vision becomes “lost”. “Beauty”, is something that is individually graded, but “uniformity” (regardless of content quality) will always be appreciated.
Ningen keisei “The formation of a true human being of the highest human values”
Often considered “esoteric”, (to myself) this means providing “positive” thoughts/idea's/concept's from what the piece is attempting to convey.
All of these guidelines can also be be summarized by the word “Focus”, not necessarily on only “one” of them, but on “all” of them being applied, to both the piece, and with everything we do. If/when a student begins pursuing “styles” which they have no formal training, they (often) wind up “scattering” their own Focus. It should be remembered that “Shodo”, is a path that is based upon, and requires “structure”. When that structure is abandoned, brushwork can simply become a “slapping” of ink upon a piece of paper. The above “rules/guidelines” were adopted to assist/guide the student in maintaining their own “Focus”.