利口

1. Origins, structure, and basic meaning

• Structure: 利口 (りこう) is a na-adjectival expression for a person or animal being quick to understand and smart.
• Basic usage: 利口で合図を覚えた predicates the dog’s cleverness and links it to learning signals, while 利口なだけでなく evaluates a sister’s intelligence alongside consideration for others.

2. Common pitfalls and similar expressions

• Connective で and attributive な
  • 利口で connects the first predication to its result, while 利口な attaches before the だけ construction. The evaluated subjects are a dog and a person respectively.