Union sentences with a colon consist of two or more parts, each of which has a certain meaning. It is from him that the choice of a punctuation mark depends.
Colon in a unionless sentence
1. This punctuation mark is placed if the next sentence (or a group of them) indicates the reason why something was said in the first one. For example: “Andrei failed to arrange his brother as a master’s apprentice: they didn’t take such young people there”, “Sailors stayed to sleep on the deck: it became unbearably stuffy downstairs”
2. A colon in an all-union compound sentence is applied when the next sentence (or group thereof) reveals the essence of the entire first sentence or one of its members. Then between its components instead of a punctuation mark it is easy to insert namely (explanatory union). For example: "The house began to make noise slowly: at one end the door creaked; footsteps began to be heard in the courtyard; someone sneezed in the room," "Soon I also found happiness: my daughter returned to me." A colon is placed between several parts of such a sentence even when the first contains pronouns.
The concrete meaning of the words is
so, one, such, such , etc., the second part is interpreted. For example: "All the people there are like this: a gossip sits on a gossip and drives a gossip," "One thing was clear: he would never come back." It should also be clarified that in a complex non-union sentence, one pronoun word is fully explained in the second part. This is the case when a colon is used after it. For example: "I ask you only about one thing: decide faster." And in a simple non-union sentence, it is supplemented only by an explanatory word, after it a dash is put. For example: "In relations with strangers, the father demanded only one thing - to keep decency."
3. The colon in the non-union sentence is also used when the first sentence contains the verbs to look back, look, listen , as well as those that indicate an action warning about what will be stated below. Instead of a punctuation mark, between its parts it is easy to insert a union that or even a combination of words: and noticed that; and saw that . Sometimes in these cases they put a dash, although it is preferable to put a colon. For example: "I looked out the window: stars appeared in the clear sky," "I looked around: triumphed around and the night reigned." In these examples, the second sentence reveals the meaning of the first, complements it.
4. The colon in an all-union compound sentence is also applied if the next part is presented as a direct question. For example: "I walked now, I spoke with you and thought all the time: why don’t they change?", "You better confess to me this: is it true that you are still in love with her?"
Colon in unionless sentence in newspaper headlines
When the title of an article splits into two parts - this is a separate case of setting this punctuation mark. The naming theme - the first part of the heading - indicates the problem as a whole, the person, the scene, etc. The continuation of the name already specifies what was mentioned at the beginning. For example: "Children: welcome and not so."