肩

1. Origins, structure, and basic meaning

• Structure: 肩 is read as かた and is a noun for the shoulder, the upper part of the body where the arm joins the torso.
• Basic usage: The body part becoming painful appears in 肩が痛くなる, while the target of a pat appears in 肩をたたく.

2. Common pitfalls and similar expressions

• が and を
  • 肩が makes the shoulder the subject whose condition changes, while 肩を marks it as the object of an action such as patting.
• Difference from 腕
  • 腕 is the arm extending from the shoulder toward the hand, while 肩 is the upper part where the arm joins the torso.