The differences between 反而 (fǎn'ér) and 相反 (xiāngfǎn) are pretty clear. 反而 is an adverb, while 相反 is an adjective and also a conjunction, and this determines how they are used grammatically.
Position in a Sentence
Structure
相反 normally starts a sentence, and when used should be followed with a comma. As an adverb, 反而 is not so set apart from the rest of the sentence, and should not be followed by a comma.
Examples
- 这样 做 帮 不了 他 ，相反，还 会 害 了 他。.
- 这样 做 不但 帮 不了 他，反而 会 害 了 他。.
Differences in Meaning
反而 is used in the context of the speaker expecting some kind of turning point. 相反 is for similar things that have a different aspect. 反而 conveys that the difference between what was expected and what actually happened was quite large. 相反 isn't as strong.
Structure
Situation，相反，The Opposite of the Situation
Expectation，反而 + The Opposite of Expectation
Examples
- 好好 工作 就 会 升职，相反，不 好好 工作 是 不 会 升职 的。.
- 老板 没有 生气，反而 表扬 了 我。.
- 老板 没有 生气，相反，他 还 表扬 了 我。.
相反 can act as an attribute
相反 is an adjective, and of course it can also be an attribute. Just make sure to add a 的 after it. 反而 cannot be used this way.
Structure
Examples
- 这 是 两 个 完全 相反 的 结果。 These are two completely opposite results.
- 你 应该 朝 相反的 方向 走。 You should go down a different path.
相反 can be the predicate
相反, like all other adjectives, can be placed after the subject as the predicate of the sentence.
Structure
Subj. + 相反
A 和 / 跟 B ＋ 是 ＋ 相反的
Examples
- 这 两 种 艺术 的 表现 形式 相反。 These two art pieces have completely different forms.
- 我们 的 看法 是 相反 的。 Our perspectives are not the same.
- 老板 的 想法 跟 我 的 相反。 The boss's way of thinking and mine don't match up.
- 现在 的 观念 和 以前 的 相反。 The views of today are different from what they were in the past.
See Also
Sources and further reading
Books
- 对外汉语教学语法释疑201例 (相反 vs 反而 p.184)
- 现代汉语八百词（增订本） (反而p.199 相反p.574)
- 现代汉语虚词例释 (反而p.172 相反p.504)
- 卓越汉语－公司实战篇 (pp. 19-20)
Dictionaries
- 现代汉语词典（第5版） (相反p.1484 反而p.377)