Another problem for Polish people! Independence Day (no 'the') is in July, ON 4th July (But we say the 4th of July.) Tomorrow is Thursday, 1st December (But we say Thursday, the first of December.) We use 'in' for months and years (periods of time) but 'on' for when a particular action takes place - it refers to a specific day. We have Andzejki on 29th November. But AT for holiday periods and weekends - 'I will not be working at Christmas!' Hope this helps Bob