be·cause (bĭ-kôz′, -kŭz′)
For the reason that; since.
[Middle English, short for bi cause of; see because of.]
Usage Note: A traditional rule holds that the construction the reason is because is redundant, and should be avoided in favor of the reason is that. The usage is well established, however, and can be justified by analogy to constructions such as His purpose in calling her was so that she would be forewarned of the change in schedule or The last time I saw her was when she was leaving for college. All three constructions are somewhat less than graceful, however. · A favorite rule of schoolteachers (but curiously absent from the tradition of usage commentary) is that a sentence must not begin with because. Sometimes, however, because is perfectly appropriate as the opening word of a sentence. In fact, sentences beginning with because are quite common in written English, as in this example from Frank Conroy: "Because he was a prodigy, he was somewhat isolated within his own generation." · Another rule states that one should not use a clause beginning with because as the subject of a sentence, as in Just because he thinks it a good idea doesn't mean it's a good idea. This construction is perfectly acceptable, but it carries a colloquial flavor and may best be reserved for informal situations. See Usage Note at as1.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
because (bɪˈkɒz; -ˈkəz)
1. (subordinating) on account of the fact that; on account of being; since: because it's so cold we'll go home.
2. because of (preposition) on account of: I lost my job because of her.
[C14 bi cause, from bi by + cause]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
be•cause (bɪˈkɔz, -ˈkɒz, -ˈkʌz)
for the reason that; due to the fact that. Idioms:
because of, by reason of; due to.
[1275–1325; Middle English bi cause literally, by cause]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
You use because when you are giving the reason for something.
If someone asks a question beginning with 'Why?', you can reply using because.
'Why can't you come?' 'Because I'm too busy.'
You use because with a reason clause when you are explaining a statement.
I couldn't see Elena's expression, because her head was turned.
Because it's an area of outstanding natural beauty, you can't build on it.
When you use because at the beginning of a sentence, don't put a phrase such as 'that is why' at the beginning of the second clause. Don't say, for example, 'Because you have been very ill, that is why you will understand how I feel'. You simply say 'Because you have been very ill, you will understand how I feel'.
2. 'because of'
You can use because of before a noun phrase when you are giving the reason for something.
Many couples break up because of a lack of money.
Because of the heat, the front door was open.
Collins COBUILD English Usage © HarperCollins Publishers 1992, 2004, 2011, 2012