In [Numbers 12][n12], Miriam and Aaron together "speak against" Moses:

> 1 And **Miriam and Aaron** spake against Moses because of the Ethiopian woman whom he had married: for he had married an Ethiopian woman.
2 And **they said**, Hath the Lord indeed spoken only by Moses? hath he not spoken also by us? And the Lord heard it. (KJV)

And yet the punishment appears to fall on Miriam alone:

> 10 And the cloud departed from off the tabernacle;  and, behold, **Miriam became leprous**, white as snow:  and **Aaron looked upon Miriam**, and, behold, **she was leprous**.   11 And Aaron said unto Moses, Alas, my lord, I beseech thee, lay not the sin upon **us**, wherein **we** have done foolishly, and wherein **we** have sinned.   12 **Let her not be as one dead**, of whom the flesh is half consumed when he cometh out of his mother's womb.   13 And Moses cried unto the LORD, saying, Heal **her** now, O God, I beseech thee.   14 And the LORD said unto Moses, If her father had but spit in **her** face, should she not be ashamed seven days?  let **her** be shut out from the camp seven days, and after that let her be received in again.   15 And **Miriam was shut out** from the camp seven days:... (KJV)

Why does God punish Miriam only, and not Miriam *and* Aaron?

[n12]: https://www.biblegateway.com/passage/?search=Numbers%2012&version=NIV;KJV;WLC