Then in the principal proposition is sometimes used as a correlative of when in the clause. Then is not a necessary word, but if the clause is long, then is useful in informing the reader that the principal proposition is about to begin.
2. “Man should forget his anger before he lies down to sleep.”—De Quincey. Before (sometimes ere) makes a sentence signify that the main action occurs in time previous to the time of the action expressed in the clause.
3. “After I had learned to row in the gondolier fashion, I voyaged much in the lagoon with my boat.”—Howells. After makes the sentence signify that the main action occurred later than the action in the clause.
Sentences in which temporal clauses are introduced by when, before, ere, or after, only establish for us the proper relation between two points of time; viz., that one point coincides with another, is antecedent to it, or subsequent to it. If we wish to denote the duration of a state or an activity, we introduce the temporal clause by while, since, till, or until.
4. “While they sat at dinner, a great fire of sunset spread over the west.”—Black. While signifies during the time that.
5. “Since you were at Oulton, my wife has been growing worse and worse in health, and more and more eccentric and crotchety.”—Shorthouse. Since signifies from the time that.
6. “Till men have been some time free, they know not how to use their freedom.”—Macaulay. Till signifies up to the time that.
7. If we wish to be exact about the time that something begins, we introduce the temporal clause by the phrase as soon as, or soon as, which phrase may be considered one connective,—“As soon as it is convenient to you, I shall be glad for you to leave this sombre place.”—Shorthouse.
8. As is frequently used either for when or for while.
“The boat had touched the silver strand,