“倘若” 和 “假如” 有区别吗？ 有，在下面第一个句子中，【倘若】可以替换为【即使】，但不适合换成【假如】，会显得不自然。 下面第二个句子中不适合用【倘若】。 In the first sentence below, it's unnatural to use 假如. In the second sentence below, it's unnatural to use 倘若. [倘若]他成了功，他也不能为我民族造幸福。 [假如]从中选择，您会选择做谁？

It means the same thing - if. But because I've done a lot of reading recently, I found that 倘若 is commonly used in legal documents of Hong Kong. We would say 假如 a lot, informally. In formal writing or documents, 假如 would be replaced by 若 or 如.

倘若和假如都有如果，假设的意思，只不过倘若多用于书面语，假如则在日常口语中比较常见