maintain

Compared meaning: keep something going or unchanged (verb).

比较义项：维持，使保持原状或持续（动词）。

• maintain 本词

  Maintain emphasizes ongoing care or effort to keep something in good condition or unchanged, often used for households, equipment, standards, or relationships.

  maintain强调通过持续的照料或努力，使某物保持良好状态或维持不变，常用于家庭、设备、标准或人际关系等。

  It takes effort to maintain a clean house with three kids.

  带着三个孩子，想维持一个整洁的家需要付出努力。

• sustain

  Sustain emphasizes keeping something alive or continuing despite difficulty, pressure, or scarce resources, often used for crops, life, or economies.

  sustain强调在困难、压力或资源匮乏的情况下使某事物得以维持或延续，常用于农作物、生命或经济等。

  Farmers work hard to sustain their crops during dry seasons.

  农民们在干旱季节努力维持农作物的生长。

Maintain and sustain both mean to keep something going. Maintain stresses steady care to keep something unchanged, as with houses. Sustain stresses keeping something alive under pressure or scarce resources, as with crops or economies. Maintain can also mean insisting something is true; not compared.

这两个词在这个义项上都表示“维持、使继续保持某种状态”，但maintain更强调通过持续的照料或努力使事物保持良好状态或不变，常用于房屋、设备、标准、关系等；sustain更强调在压力、困难或资源有限的情况下使某事物得以延续，常用于农作物、生命、经济等。这里不比较maintain的“主张，坚持（观点）”这一义项。

Compared meaning: state an opinion firmly (verb).

比较义项：坚称、坚持主张（动词）。

• maintain 本词

  Used when someone keeps insisting that a claim or opinion is true, especially when it is doubted or opposed, often about one's own innocence.

  用于某人尽管受到怀疑或反对，仍反复坚称某种说法或观点属实，常用来表示坚称自己无罪。

  Despite the evidence against him, he continued to maintain that he was innocent.

  尽管有对他不利的证据，他依然坚称自己是清白的。

• assert

  Conveys stating something with confidence and authority, often to defend oneself or stand up for one's own rights.

  表示自信而有力地表明观点或立场，常用于为自己辩护、坚持自身权利。

  She finally learned to assert herself and speak up in meetings.

  她终于学会了在会议中坚定自信地表达自己并主动发言。

Maintain and assert both mean stating an opinion firmly. Maintain stresses repeating a claim despite doubt, often about one's innocence. Assert stresses stating a view confidently, often to defend oneself or one's rights. Maintain can also mean keeping up a house; not compared here.

这两个词都表示坚定地陈述某种看法：maintain 强调在受到怀疑或反对时依然反复坚持自己的说法，常用于坚称清白或坚持某种立场；assert 强调自信而有力地表明观点或立场，常用于为自己辩护、维护权利。这里不比较 maintain 的“维持、保养”义，如 maintain a house。