Here's why:
* "As" as a conjunction: While "as" can sometimes act as a conjunction, it usually introduces a subordinate clause that describes a simultaneous action or state. For example: "As the sun set, the sky turned orange."
* "As" as a preposition: "As" is more commonly used as a preposition, meaning it introduces a phrase that shows a relationship between a noun and another part of the sentence. For example: "I know her as a friend."
* "As" in comparisons: "As" is also used in comparisons: "He is as tall as his brother."
To use "as" as a conjunction, it usually needs to be followed by a clause that provides more information about the main clause.
Here are some examples of "as" used as a conjunction:
* As the train pulled into the station, I saw her waving. (This clause describes the simultaneous action of the train pulling in and seeing her waving.)
* As the days grew shorter, the weather turned colder. (This clause describes the simultaneous actions of the days shortening and the weather getting colder.)
However, it is important to note that "as" can be used in conjunction with other words to create a conjunction, such as "as well as" or "as long as".
For example:
* As well as being a good cook, she is also a talented musician. (This sentence uses "as well as" as a conjunction to connect two ideas.)
* As long as you finish your homework, you can watch TV. (This sentence uses "as long as" as a conjunction to connect the condition of finishing homework with the reward of watching TV.)