が

1. Origins, structure, and basic meaning

• Structure: Attach が to the first clause's predicate to connect another clause. Polite sentences use forms such as ですが or ますが.
• Basic usage: It acknowledges the first point while adding a different circumstance or contrasting assessment.
  • この店は小さいですが、料理はおいしいです。 contrasts the shop's size with the quality of its food.

2. Common pitfalls and similar expressions

• Distinct from subject marking
  • In 料理がおいしい, が follows a noun and marks the subject. In 小さいですが, が connects clauses, so its role is different.
• Plain nouns and na-adjectives
  • Plain affirmative nonpast forms such as 学生だが and 静かだが retain だ. Forms such as 高いが and 行くが do not take an added だ.
• Not always an opposite statement
  • It can also introduce background or soften an opening, as in 質問がありますが. What follows need not be the exact opposite.