It is important to understand that "by" generally indicates a method or means, while "because" introduces a reason or cause. Here are some sentences to illustrate the differences:

Using "by":

• "She succeeded by working hard every day."

        Here, "by" indicates the method through which she achieved success.

• "The package was delivered by the courier."

        "By" shows the means through which the package was delivered.

• "By saving money each month, he was able to buy a new car."

        "By" introduces the method he used to afford the car.

Important Note

If you notice, in the second sentence, you cannot use 'because'. The reason is simple - The courier was the 'method' used to deliver the package. It was not the reason! Here are some more examples to clarify the same.

Using "because":

• "She succeeded because she worked hard every day."

        "Because" introduces the reason for her success.

• "The game was canceled because of the rain."

        "Because of" provides the reason for the game's cancellation.

• "He was happy because he received good news."

        "Because" explains why he felt happy.

Important Note

If you notice, in the first sentence, which is the same - by and because can be used because hardwork was both the reason behind the success and the method used to achieve success. But in the second and third sentences, you can only use 'because' since we are talking about the reason and not the method.

Here are some more examples

• By reading books, you can improve your vocabulary.
  

        "By" is followed by the gerund "reading," indicating the method of improving vocabulary.

• The letter was sent by express mail.

        "By" is followed by the noun phrase "express mail," showing the means of sending the letter.

• He keeps fit by jogging every morning.

        "By" precedes the gerund "jogging," which describes the method he uses to stay fit.

• She is happy because she received a promotion.

    "Because" introduces the clause "she received a promotion," which explains the reason for her happiness.

• The game was postponed because it was raining.

    Here, "because" is followed by the clause "it was raining," providing the reason for the postponement.

• They decided to stay indoors because the temperature was dropping.

    "Because" precedes the clause "the temperature was dropping," explaining why they chose to stay indoors.

Final Word To Help Understand The Difference Between 'Because' and 'By'

Understanding these structural differences is essential for correctly using "by" and "because" in sentences. By recognizing whether you're indicating a method/means or providing a reason/cause, you can choose the appropriate word and construct your sentence accordingly.