～つ

1. Origins, structure, and basic meaning

• Structure: In this native counting series, forms from 一つ through 九つ end in つ. Ten is written 十 and read とお, without つ.
• Basic usage: It counts objects or items from one through ten.
  • りんごが三つあります。 counts three apples.

2. Common pitfalls and similar expressions

• Whole-form readings
  • 三つ is みっつ, 五つ is いつつ, and 六つ is むっつ. Do not build these by attaching つ to the usual Sino-Japanese number readings.
• Distinct from counting people
  • Three people are counted as 三人. Do not use the same counter interchangeably for objects and people.
• Asking a quantity and using other counters
  • Use いくつ to ask how many.
  • An object such as an apple can be counted with つ or with another counter such as 個, so an object need not have only one possible counter.