一方だ

1. Origins, structure, and basic meaning

• Structure: 一方だ（いっぽうだ） follows a dictionary-form change verb and expresses a continuing trend in one direction.
• Basic usage: この地域では空き家が増える一方だ。 emphasizes the continuing increase in vacant houses in the area.

2. Common pitfalls and similar expressions

• Express the change, not just the state
  • Use a change verb as in 高くなる一方だ rather than the static 高い一方だ. It can also describe a downward trend, as in 減る一方だ.
• The clause relationship with 一方で
  • 会員は増える一方だ ends with a statement about growing membership. 会員は増える一方で収入は減っている instead connects and compares two aspects, membership and income.