The difference between Before and By
When used as prepositions, before means earlier than (in time), whereas by means near or next to.
When used as adverbs, before means at an earlier time, whereas by means along a path which runs by the speaker.
Before is also conjunction with the meaning: in advance of the time when.
By is also noun with the meaning: a pass.
By is also adjective with the meaning: out of the way, subsidiary.
check bellow for the other definitions of Before and By
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Before as a preposition:
Earlier than (in time).
Examples:
"I want this done before Monday."
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Before as a preposition:
In front of in space.
Examples:
"He stood before me."
"We sat before the fire to warm ourselves."
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Before as a preposition:
In the presence of.
Examples:
"He performed before the troops in North Africa."
"He spoke before a joint session of Congress."
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Before as a preposition:
Under consideration, judgment, authority of (someone).
Examples:
"The case laid before the panel aroused nothing but ridicule."
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Before as a preposition:
In store for, in the future of (someone).
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Before as a preposition:
In front of, according to a formal system of ordering items.
Examples:
"In alphabetical order, "cat" comes before "dog", "canine" before feline"."
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Before as a preposition:
At a higher or greater position than, in a ranking.
Examples:
"An entrepreneur puts market share and profit before quality, an amateur intrinsic qualities before economical considerations."
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Before as an adverb:
At an earlier time.
Examples:
"I've never done this before."
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Before as an adverb:
In advance.
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Before as an adverb:
At the front end.
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By as a preposition:
Near or next to.
Examples:
"The mailbox is by the bus stop."
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By as a preposition:
At some time before (the given time), or before the end of a given time interval.
Examples:
"Be back by ten o'clock!  We will send it by the first week of July."
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By as a preposition:
Through the action or presence of.
Examples:
"The matter was decided by the chairman.  The boat was swamped by the water.  He was protected by his body armour."
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By as a preposition:
Existing through the authorship etc. of.
Examples:
"There are many well-known plays by William Shakespeare"
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By as a preposition:
Through the action of, caused by, responsibility for; by dint of.
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By as a preposition:
Involving/using the means of.
Examples:
"I avoided the guards by moving only when they weren't looking."
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By as a preposition:
Examples:
"The electricity was cut off, so we had to read by candlelight."
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By as a preposition:
.
Examples:
"I sorted the items by category.  By the power vested in me, I now pronounce you man and wife."
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By as a preposition:
With a change of.
Examples:
"Our stock is up by ten percent."
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By as a preposition:
Examples:
"We went through the book page by page.  We crawled forward by inches."
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By as a preposition:
According to.
Examples:
"He cheated by his own admission."
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By as a preposition:
With the authority of.
Examples:
"'By Jove! I think she's got it!  By all that is holy, I'll put an end to this."
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By as a preposition:
Examples:
"It is easy to invert a 2-by-2 matrix.  The room was about 4 foot by 6 foot.  The bricks used to build the wall measured 10 by 20 by nowrap 30 cm."
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By as a preposition (horse breeding):
Examples:
"She's a lovely little filly, by Big Lad, out of Damsel in Distress."
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By as an adverb:
Along a path which runs by the speaker.
Examples:
"I watched as it passed by."
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By as an adverb:
In the vicinity, near.
Examples:
"There was a shepherd close by."
"The shop is hard by the High Street."
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By as an adverb:
To or at a place, as a residence or place of business.
Examples:
"I'll stop by on my way home from work."
"We're right near the lifeguard station. Come by before you leave."
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By as an adverb:
Aside, away.
Examples:
"The women spent much time after harvest putting jams by for winter and spring."
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By as an adjective:
Out of the way, subsidiary.
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By as a noun (card games):
A pass