I have seen 'since', 'because', 'as', 'due to', and 'for the purpose of' in different text and I was wondering what is the difference between them.
Looking into Longman dictionary, I found very similar definitions for the 5 of them. Here are the definitions:
Used to give the reason for something:
E.g., Since you are unable to answer, perhaps we should ask someone else.
Used when you are giving the reason for something:
E.g. 1, We didn't enjoy the day because the weather was so awful.
E.g. 2, Because you're not old enough.
E.g. 3, Hubert never experienced any fear, and this was partly because he was not particularly intelligent.
E.g. 4, Many exam candidates lose marks simply because they do not read the questions properly.
E.g. 5, I decided to go with them, mainly because I had nothing better to do.
used to state why a particular situation exists or why someone does something:
E.g. 1, As it was getting late, I turned around to start for home.
E.g. 2, We asked Philip to come with us, as he knew the road.
because of something:
E.g. 1, The court of inquiry ruled that the crash was due to pilot error.
E.g. 2, She has been absent from work due to illness.
E.g. 3, The restaurant's success was due largely to its new manager.
E.g. 4, Attendance at the meeting was small, due in part to (=partly because of) the absence of teachers.
for/with the purpose of doing something:
E.g. 1, Troops were sent solely for the purpose of assisting refugees.
E.g. 2, He came here with the purpose of carrying out the attack.