更ける

1. Origins, structure, and basic meaning

• Structure: 更ける (ふける) is an ichidan intransitive verb for the night advancing and becoming late.
• Basic usage: 夜が更けるにつれて describes streets quieting as the night grows late, while 夜も更けていた shows that it had already become late during an absorbing conversation.

2. Common pitfalls and similar expressions

• Progressive reference and attained lateness
  • 夜が更ける tracks the advance of nighttime, while 夜も更けている describes a substantially advanced state. These inputs do not support a sense of a season deepening.