足す

1. Origins, structure, and basic meaning

• Structure: 足す (たす) is a transitive verb for supplementing an amount or adding numbers. The examples use past and dictionary forms.
• Basic usage: A little salt is added after tasting; four is added to three to produce seven.

2. Common pitfalls and similar expressions

• Addition for flavor adjustment and mathematical addition
  • The added item is 塩を; arithmetic uses 三に四を to mark base and addend. One result is sensory adjustment and the other exact quantity.