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Strokes (simplified Chinese: 笔画; traditional Chinese: 筆畫; pinyin: bǐhuà) are the smallest structural units making up written Chinese characters. In the act of writing, a stroke is defined as a movement of a writing instrument on a writing material surface, or the trace left on the surface from a discrete application of the writing implement.[1] The modern sense of discretized strokes first came into being with the clerical script during the Han dynasty.[2] In the regular script that emerged during the Tang dynasty—the most recent major style, highly studied for its aesthetics in East Asian calligraphy—individual strokes are discrete and highly regularized. By contrast, the ancient seal script has line terminals within characters that are often unclear, making them non-trivial to count.
Study and classification of strokes is useful for understanding Chinese character calligraphy, ensuring character legibility. identifying fundamental components of radicals, and implementing support for the writing system on computers.
Evolution
The terminals of the individual marks in ancient character forms are often unclear, and it is sometimes nontrivial to count them. The modern motion of discretized strokes did not fully emerge until clerical script:[3]
| Oracle | Bronze | Seal | Clerical | Regular | ||
|---|---|---|---|---|---|---|
| Large | Small | Traditional | Simplified | |||
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Purpose
The study and classification of strokes is used for:
- understanding Chinese character calligraphy – the correct method of writing, shape formation and stroke order required for character legibility;
- understanding stroke changes according to the style that is in use;
- defining stroke naming and counting conventions;
- identifying fundamental components of Han radicals; and
- their use in computing.
Formation
When writing Han radicals, a single stroke includes all the motions necessary to produce a given part of a character before lifting the writing instrument from the writing surface; thus, a single stroke may have abrupt changes in direction within the line. For example:
(Vertical / shù) is classified as a basic stroke because it is a single stroke that forms a line moving in one direction.
(Vertical – Horizontal – Vertical / shù zhé zhé) is classified as a compound stroke because it is a single stroke that forms a line that includes one or more abrupt changes in direction. This example is a sequence of three basic strokes written without lifting the writing instrument such as the ink brush from the writing surface.
Direction
All strokes have direction. They are unidirectional and start from one entry point. As such, they are usually not written in the reverse direction by native users. Here are some examples:
Types
CJK strokes are an attempt to identify and classify all single-stroke components that can be used to write Han radicals. There are some thirty distinct types of strokes recognized in Chinese characters, some of which are compound strokes made from basic strokes. The compound strokes comprise more than one movement of the writing instrument, and many of these have no agreed-upon name.
Basic strokes
A basic stroke is a single calligraphic mark moving in one direction across a writing surface. The following table lists a selection of basic strokes divided into two stroke groups: simple and combining. "Simple strokes" (such as Horizontal / Héng and Dot / Diǎn) can be written alone. "Combining strokes" (such as Bend / Zhé and Hook / Gōu) never occur alone, but must be paired with at least one other stroke forming a compound stroke. Thus, they are not in themselves individual strokes.
| English Name | Name in PRC (pinyin and simp.) |
Name in ROC (pinyin and trad.) |
Name in Japan | Name in Vietnam | CJK stroke |
Meaning of Chinese name (Japanese name, if different) |
Additional description |
|---|---|---|---|---|---|---|---|
| Simple strokes | |||||||
| Dot | Diǎn, 点 | Diǎn, 點 | Ten, 点 | Chấm 枕 |  |
"Dot" | Tiny dash, speck. |
| Horizontal | Héng, 横 | Héng, 橫 | Yoko, 横 | Sổ ngang 𬃈昂 |  |
"Horizontal" | Rightward stroke. |
| Vertical | Shù, 竖 | Shù, 豎 | Tate, 豎 | Sổ dọc 𬃈𫆡 |  |
"Vertical" | Downward stroke. |
| Upward horizontal | Tí, 提 | Tiāo, 挑 | Hane, 跳 | Hất 迄 |  |
"Rise" ("Jump") |
Flick up and rightwards. |
| Press | Nà, 捺 | Nà, 捺 | (Migi) Harai, (右)払 | Mác 莫 |  |
"Press down" ("(Right) Sweep") |
Falling rightwards (fattening at the bottom). |
| Throw | Piě, 撇 | Piě, 撇 | (Hidari) Harai, (左)払 | Phẩy 𢵪 |  |
"Throw away" ("(Left) Sweep") |
Falling leftwards (with slight curve). |
| Combining strokes | |||||||
| Bend | Zhé, 折 | Zhé, 折 | Ore, 折 | Gập 岋 |  |
"Bend, fold" | Indicates change in stroke direction, usually 90° turn, going down or going right only. |
| Hook | Gōu, 钩 | Gōu, 鈎(鉤) | Kagi, 鉤 | Móc 鈢 |  |
"Hook" | Appended to other strokes, suddenly sharp turning before crash stopping. |
| Clockwise curve | Wān, 弯 | Wān, 彎 | (Hidari) Sori, (左)反 | Cong 𢏣 |  |
"Curve" | Tapering curved line, usually concave left (convex outward right). |
| Anticlockwise curve | Wān, 弯; Xié, 斜 | Qū, 曲 | (Migi) Sori, (右)反 | Nghiêng 迎 | ㇄;  |
"(Right) curve"; "Slant" | Curved line, usually concave right (convex outward left). |
Note, the basic stroke Diǎn "Dot" is rarely a real dot. Instead it usually takes the shape of a very small line pointing in one of several directions, and may be long enough to be confused with other strokes.
Compound strokes
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A compound stroke (also called a complex stroke) is produced when two or more basic strokes are combined in a single stroke written without lifting the writing instrument from the writing surface. The character 永 (pinyin: yǒng) "eternity", described in more detail in § Eight Principles of Yong, demonstrates one of these compound strokes. The centre line is a compound stroke that combines three stroke shapes in a single stroke.
- Basics for making compound strokes[5]
In most cases, concatenating basic strokes together form a compound stroke. For example, Vertical / Shù combined with Hook / Gōu produce 
(Vertical–Hook / Shù Gōu). A stroke naming convention sums the names of the basic strokes, in the writing order.
An exception to this applies when a stroke makes a strictly right-angle turn in the Simplified Chinese names. Horizontal 
(Héng) and Vertical 
(Shù) strokes are identified only once when they appear as the first stroke of a compound; any single stroke with successive 90° turns down or to the right are indicated by a Bend 折 (pinyin: zhé). For example, an initial Shù followed by an abrupt turn right produces 
(Shù Zhé). In the same way, an initial Shù followed by an abrupt turn right followed by a second turn down produces 
(Shù Zhé Zhé). However, their inherited names are "Vertical–Horizontal" and "Vertical–Horizontal–Vertical". We need not to use "Bend" in the inherited names.
Nearly all complex strokes can be named using this simple scheme.
Nomenclature
Organization systems used to describe and differentiate strokes may include the use of roman letters, Chinese characters, numbers, or a combination of these devices. Two methods of organizing CJK strokes are by:
- Classification schemes that describe strokes by a naming convention or by conformity to a taxonomy; and
- Categorization schemes that differentiate strokes by numeric or topical grouping.
In classification schemes, stroke forms are described, assigned a representative character or letterform, and may be arranged in a hierarchy. In categorization schemes, stroke forms are differentiated, sorted and grouped into like categories; categories may be topical, or assigned by a numeric or alpha-numeric nominal number according to a designed numbering scheme.
Stroke Reach
| Stroke | Name In English | Chinese n. |
|---|---|---|
  |
Dot | 点 |
Benefits
Organizing strokes into a hierarchy aids a user's understanding by bringing order to an obtuse system of writing that has organically evolved over the period of centuries. In addition, the process of recognizing and describing stroke patterns promotes consistency of stroke formation and usage. When organized by naming convention, classification allows a user to find a stroke quickly in a large stroke collection, makes it easier to detect duplication, and conveys meaning when comparing relationships between strokes. When organized by numbering scheme, categorization aids a user in understanding stroke differences, and makes it easier to make predictions, inferences and decisions about a stroke.
Limitations
Strokes are described and differentiated using the criteria of visual qualities of a stroke. Because this can require subjective interpretation, CJK strokes cannot be placed into a single definitive classification scheme because stroke types lack a universal consensus on the description and number of basic and compound forms. CJK strokes cannot be placed into a single definitive categorization scheme due to visual ambiguity between strokes, and therefore cannot be segregated into mutually exclusive groups. Other factors inhibiting organization based on visual criteria are the variation of writing styles, and the changes of appearance that a stroke undergoes within various characters.
Pinyin naming convention in Unicode standard
A naming convention is a classification scheme where a controlled vocabulary is used systematically to describe the characteristics of an item. The naming convention for a CJK stroke is derived from the path mark left by the writing instrument. In this instance, the first letter of each stroke component - transliterated with pinyin pronunciation - are concatenated to form a stroke name with the sequence of letters indicating the basic strokes or stroke components used to create the CJK stroke. This system is used in the Unicode standard when encoding CJK stroke characters. In a basic stroke example, H represents the stroke named 横 (Héng); in a compound example, HZT represents 横折提 (Héng zhé tí).
While no consensus exists, there are up to 12 distinct basic strokes that are identified by a unique radical.
