Eighteen decrees in Chananiah's upper room

In the upper room of Chananiah ben Chizkiyah ben Garon the Sages voted, and that day they decreed eighteen things. The Mishnah describes a counted decision at a particular gathering where Beit Shammai held the majority. This alone does not explain the rules for deciding every dispute between the schools.

1. 1Restate the source in your own words.
2. 2Identify the central distinction and explain its significance.
3. 3Apply the distinction in the exercise without adding a ruling absent from the source.