違法

1. Origins, structure, and basic meaning

• Structure: 違法 (いほう) is a na-adjectival noun predicating that conduct or a transaction violates the law.
• Basic usage: 廃棄物を捨てるのは違法だ judges unauthorized dumping unlawful, while 取引が違法でないか asks an expert to check whether a transaction is lawful.

2. Common pitfalls and similar expressions

• Affirmative judgment and negative question
  • 違法だ affirmatively judges conduct unlawful, whereas 違法でないか is an embedded negative question seeking confirmation. The latter does not itself establish legality.