行 = 彳 + 亍. The Unihan structure splits 行 into its left half 彳 (chì — small step, the step-radical that opens dozens of motion characters) and its right half 亍 (chù — also a step-element). Two halves of a stride. But the older and more illuminating reading is pictographic: 行 originated as a drawing of a four-way crossroads seen from above — two roads intersecting at right angles. The Shuōwén Jiězì 说文解字 already gives this reading: 行 = 人之步趋也 "the place where people walk and hurry."

This is why 行 is its own radical — it heads a small but consistent family of characters about roads and travel: 街 jiē (street), 衍 yǎn (to flow; to spread along a path), 衢 qú (a thoroughfare). Wherever 行 sits in a character, you should hear roads and motion.

From crossroads the meanings radiate naturally: a place where one walks (a road) → the act of walking → motion in general → going through with something → carrying out an action → conduct → a person's way of moving through life. And, by a parallel route from the same root: a row of things lined up (like a row of stalls along a road) → a category of trades → a profession → a business firm. Two distinct readings — xíng and háng — preserve the split.

The verbal sense of 行 stretches naturally from walking through doing into conduct — the moral domain. The Confucian tradition is built on this stretch. A person's 德行 (moral conduct) is what their 德 looks like in motion. 言行 yánxíng — words and conduct — is the standard pairing for evaluating sincerity (do they match?). 言行不一 "words and conduct don't match" is the standard accusation of hypocrisy. 品行 pǐnxíng (character-conduct) is what schools and employers ask about in evaluations.

This moral 行 is also why Confucius's most-quoted line on learning uses it: 三人行，必有我师焉 "where three are walking, one of them must be my teacher" — meaning that everyone you meet has something to teach you, if you watch their conduct closely.

The háng reading preserves a different descendant of the original "crossroads" sense: a row of things lined up along a road. The classical image is a market street where each row (行 háng) of stalls dealt in a particular commodity — the silver-changers' row, the silk row, the salt row. Each row became a trade-name, each trade became a profession, and each profession (in modern Chinese) became a business firm. So the same character that names "the silk-merchants' row" came to name "a silk firm" and ultimately, by extension, "a bank" — 银行 yínháng, the silver-row.

This is also why 内行 nèiháng (literally "inside-the-row") means an expert and 外行 wàiháng ("outside-the-row") means an amateur — you are inside or outside the trade.

The whole character is a four-way crossroads seen from above — two roads intersecting. From that one image, two whole vocabularies unfold: xíng, the verb-side — what one does on the road (walk, go, act, conduct oneself), and háng, the noun-side — what lines up along the road (rows of stalls, trades, firms). When you see 行 in a new compound, ask: is this character naming an action (xíng) or a row/trade (háng)? The answer is almost always clean.

The single trap to learn first: 银行 = yínháng, not yínxíng. A bank is a row, not a verb. Get this one right and most of the rest follows.