Hey Ovtolevks, how are you? 1) ''Before'': When ''before'' is used in the middle of a sentence, it's not usually preceded by a comma. However, a comma should be present in a clause should the word ''before'' be placed at the beginning of it. E.g.: ''The train had left before he arrived at the station.'' E.g.: ''Before I go, I must phone my parents.'' 2) ''After'': if you intend to say that someone does something after doing another, you should then consider two kinds of situations: one related to a statement or description about an event or situation; and the other related to a statement containing a sense of ''demand''. For the former, there is no need for commas; whereas for the latter, the usage of commas shall be required. E.g.: ''After leaving school he worked as an accountant.'' (in this case, you can notice that no commas are needed as the sentence refers to a statement or description about an event) E.g.: ''After completing and signing the form, please return it to me.'' (in this case, you are ''demanding'' something from someone, so you should use a comma in order to express your idea more clearly to whom is listening). 3) ''Because'': The usage of commas is required should you wish to use ''because'' with a reason clause when you are either explaining a statement or giving the reason for something. For the latter, the idiom ''because'' shall be shifted to ''because of''. E.g.: ''Because it's an area of outstanding natural beauty, you can't build on it.'' E.g.: ''Because of the heat, the front door was open.'' 4) ''Since''/''as'': When either of these words introduces a sentence and is used in the same sense as ''because'', then the usage of commas in the middle of the sentence is required. E.g.: ''As he had been up since 4 a.m., he was now very tired.'' E.g.: ''Since I hadn't heard from you, I decided to give you a call.'' Hope that helps!!! Should you have any further questions, do not hesitate to contact me. I shall be pleased to help.