Classical grammar words in the Dao De Jing
则 zé
In the Dao De Jing, 则 (zé) is mostly the conjunction “then” (31 times), linking a condition to its result; once it is a verb, “to follow, take as a model” (1).
则 links two clauses: when the first holds, the second follows. Where 故 “therefore” draws a conclusion from what has been said, 则 states what happens once a condition is met: 少则得，多则惑 (chapter 22), “with few there is attainment, with much there is confusion.” As a noun 则 means “rule, standard”, and from that it can be a verb, “to take as a rule, to follow”.
Modern Chinese says 就 or 那么 for the conjunction; 则 itself lives on in formal writing and in words such as 规则 “rule” and 原则 “principle”.
则 as “then”
Pattern A 则 B
A conjunction between a condition and its result, “then, and so”. The condition comes first, often with no word for “if”: 为无为，则无不治 (chapter 3), “Act without acting, and nothing will be out of order.” Chapter 22 strings short pairs: 曲则全，枉则直, “The bent is made whole, the crooked is straightened.” At the head of a line it picks up a condition stated just before: 则不可得志于天下矣 (chapter 31), “cannot achieve his aims in the world.”
31 times in 25 lines.
为无为，则无不治。
Act without acting, and nothing will be out of order.
Chapter 3, line 7曲则全，枉则直，
The bent is made whole, the crooked is straightened,
Chapter 22, line 1洼则盈，敝则新，
the hole is filled, the worn-out is renewed,
Chapter 22, line 2少则得，多则惑。
with few there is attainment, with much there is confusion.
Chapter 22, line 3古之所谓曲则全者，岂虚言哉！
The ancient saying "The bent is made whole", how can it be regarded as empty talk?
Chapter 22, line 8轻则失本，躁则失君。
Frivolousness leads to lost roots, impetuousness leads to lost rulership.
Chapter 26, line 6
Show 19 more lines
朴散则为器，
Once simplicity is dispersed, so as to craft an instrument,
Chapter 28, line 10圣人用之则为官长。
the sage, using them, sets up the heads of officials.
Chapter 28, line 11物壮则老，
Things with strength ultimately wither,
Chapter 30, line 10君子居则贵左，用兵则贵右。
At home, the noble one honors the left; at war, he honors the right.
Chapter 31, line 3则不可得志于天下矣。
cannot achieve his aims in the world.
Chapter 31, line 10则攘臂而扔之。
it rolls up its sleeves and forces them.
Chapter 38, line 8物壮则老，
Things with strength ultimately wither,
Chapter 55, line 11重积德则无不克，
accumulating virtue again and again, nothing cannot be overcome;
Chapter 59, line 4无不克则莫知其极；
when nothing cannot be overcome, no one knows one's limits;
Chapter 59, line 5则取小国；
it wins the small state;
Chapter 61, line 6小国以下大国，则取大国。
when a small state places itself below a great state, it wins the great state.
Chapter 61, line 7慎终如始，则无败事。
Be as careful at the end as at the beginning, and nothing will be spoiled.
Chapter 64, line 14夫慈以战则胜，以守则固。
With compassion, one wins in battle and holds firm in defense.
Chapter 67, line 14民不畏威，则大威至。
When the people no longer fear authority, a greater terror comes.
Chapter 72, line 1勇于敢则杀，
Bravery in daring leads to death;
Chapter 73, line 1勇于不敢则活。
bravery in not daring leads to life.
Chapter 73, line 2是以兵强则不胜，
So an army that is rigid will not win;
Chapter 76, line 6木强则兵。
a tree that is rigid will be cut down.
Chapter 76, line 7人之道则不然，
The way of people is not so:
Chapter 77, line 6
则 as “to follow, take as model”
Pattern 则 + 我 + 者
A verb, “to follow, take as a model”, used once: 知我者希，则我者贵 (chapter 70), “Those who understand me are few; those who follow me are rare and precious.” It is parallel to 知 “to understand” in the first half: both take 我 “me” as their object, and 者 turns both into “those who …”. Some readers take 则 here as “then” instead.
Once, in one line.
知我者希，则我者贵。
Those who understand me are few; those who follow me are rare and precious.
Chapter 70, line 5
How to tell them apart
In almost every line 则 sits between two clauses, each a complete thought; that is “then”. The one verb comes right before an object and is turned into “those who …” by 者, exactly like the verb in the parallel half: 知我者希，则我者贵 (chapter 70).
Compare 民不畏威，则大威至 (chapter 72), “When the people no longer fear authority, a greater terror comes”: what follows 则 is a clause of its own, not an object.