Comparing 突然 ("tu1ran2") and 忽然 ("hu1ran2")

突然和忽然都是表示事情发生得迅速和出乎意料的时间副词，但‘突然’还可以作为形容词使用，而‘忽然’只能作为副词。在语气上，‘突然’更强调突发性和冲击力，‘忽然’则更侧重于意料之外的转变。

Both 突然 and 忽然 are time adverbs indicating that something happens quickly and unexpectedly, but 突然 can also be used as an adjective, while 忽然 is only an adverb. In tone, 突然 emphasizes abruptness and impact, while 忽然 focuses more on unexpected change.

突然：1. 作为副词时，与‘忽然’用法相似，但可以修饰更多动词短语。2. 作为形容词时，可以作定语或谓语，如‘突然事件’、‘事情很突然’。3. 可以用于否定形式‘不突然’。 忽然：1. 只作为副词，表示动作或情况变化迅速、意外。2. 不可用作定语或谓语。3. 没有否定形式。 主要区别：突然可用于书面和口语，忽然较多用于口语；突然更强调短时间内的剧烈变化。

突然: 1. As an adverb, similar to 忽然 but can modify more verb phrases. 2. As an adjective, can be used as an attribute or predicate, e.g., '突然事件' (sudden event), '事情很突然' (the matter is very sudden). 3. Can be negated as '不突然'. 忽然: 1. Only as an adverb, indicating a quick and unexpected action or change. 2. Cannot be used as an attribute or predicate. 3. Has no negative form. Main difference: 突然 is used in both written and spoken Chinese, while 忽然 is more common in spoken Chinese; 突然 emphasizes a more intense change in a short period.