Q: I often hear people use “as” to mean “because,” as in the sentence, “We have to clean out our basement as we will need more room for your things.” This usage sounds horribly stuffy, though I don’t necessarily think it’s wrong per se. Are there any rules or recommendations for using “as” vs. “because” vs. “since”?
A: Both Merriam-Webster’s Collegiate Dictionary (11th ed.) and The American Heritage Dictionary of the English Language (4th ed.) say the conjunction “as” can mean “since” or “because” or “for that reason.”
But American Heritage warns that this sense of the word can be confused with the use of the conjunction “as” to mean “at the same time that”: “She was finishing the painting as I walked into the room.”
The dictionary recommends, therefore, that “as” should be preceded by a comma when used in place of “because” in the middle of a sentence: “She won’t be coming, as we didn’t invite her.”
When beginning a sentence with “as,” according to American Heritage, “one should take care that it is clear whether as is used to mean ‘because’ or ‘at the same time that.’”
The dictionary gives this example of a confusing sentence: “As they were leaving, I walked to the door.“ It’s unclear whether “I walked to the door” because, or at the same time that, “they were leaving.”
But back to your question. Dictionaries may say it’s OK to use “as” in place of “because” or “since,” but that doesn’t mean a careful writer should do it.
Bryan A. Garner, in Garner’s Modern American Usage, says this usage “should generally be avoided” because “it may be misunderstood.” I’m with Garner on this, and I don’t think sticking a comma in front of “as” will do much good, no matter what the AH lexicographers think.
On the issue of “because” vs. “since,” some sticklers insist that “since” should be used only to indicate a time period, as in “I’ve been sick since you saw me last.” I disagree.
As I say in my grammar book Woe Is I, “since” can also mean “because” or “for the reason that,” as in this sentence: “Since you asked, I’ll tell you.” People have been using “since” in this way for 500 years.
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