I had several 4 card majors yesterday. Is there a system that opens 4 card majors. Partner says no, only in response.
There are plenty of systems that open on 4-cards, I myself play one, and that is not very uncommon here. 4-card systems are commonly used to teach Bridge. Most people prefer 5-card major though, and 4-card major feels outdated these days.
A couple of the more well-known 4-card systems are