By is used to indicate proximity, the person that performs an action in a passive sentence, an action with a particular purpose, a means or method, a deadline, the person or thing that performs an action, how something is done, measurements or amounts, increasing or changing amounts over time, and describing someone's character or job. By can also be used to express being near or at the side of something. With is used to indicate using something, and beside means either next to or compared to, with next to being more common.

1. 1
BY
By isused to indicate proximity.Example:
• Can I sitby you?
• He wasstandingbyme.
• The post office isbybank.
By isusedto indicate the personthatdoessomethinginapassive voice sentence.Example:
• The microwave wasfixedbymechanic.
• The flowerswere deliveredbypostman.
• The branch office wasclosedbyheadoffice.
By isusedto indicate anactionwith a particularpurpose.Example:
• You can pass the exambypreparingforit.
• I expressedmyfeelingtowardherbywritingaletter.
• She finallybroke the recordbypure effort.
By isusedto indicate ameanor method.Example:
• Please sendthispackage toRussiabyairmail.
• I came here bysubway.
We use byto talk abouta deadline whensomethingwill happenbefore thattime. Example:
• By tomorrow
• By nextweek
• By six o'clock
• By Wednesday
• By summer
By isusedto showthe personor thingthat doessomething.Example:
• The motorcycle wasdrivenby tinybald man.
• I'm readingsome shortstories byChekhov.
• I feltfrightenedby angerinhisvoice.
By isusedto showhowsomethingisdone.Example:

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• TheytravelledacrossEurope bytrain.
• He learnedEnglishbylisteningtothe radio.
I refuse tolive bytheirrules.
By as a prepositionisusedtoexpressnearorat the side of.Example:
• A small childstoodsullenlybyherside.
• He wantedtokeepherclose byhimalways.
• The policewomanwalkedbythemwithoutsayingaword.
By isusedto showmeasurementsoramounts.Examples:
• Our office floorspace measuredtwelve metersbyten.
• Theirwageswere increasedby15 percent.
• Freelance workersare paidby hour.
• These phoneshave soldbythousand(=several thousandhave beensold).
By isusedto say that somethingincreasesorchangeswitheveryminute,hour,day,etc.Example:
• The deathtoll from the hurricane wasclimbingminute byminute.
• The credibilityof the campaignhasdeterioratedmonthbymonth.
By isusedto describe orshowwhat happenseveryminute,hour,etc. Example:
• A minute-by-minute timelineof the incident.
• The book paintsa detailed,week-by-weekportraitof hisfather'sillness.
By isusedwhendescribingsomeone'scharacter,job, etc.Example:
• She is,by nature,a sunny,positive kindof person.
• He's a plumberbytrade.
• She was,by profession,alawyer.
With
Usedto indicate "using":

3. 3
• eat witha fork;made us laughwithhisjokes.
 I wrote a letterwiththe penyougave me.
(talkenglish.coms.f.)
BESIDE
Is usedonlyasa preposition,whichmeansthereisalwaysanounfollowingit.Itmeanseither“next
to” or “comparedto,” as showninthe examplesbelow.The firstmeaning,“nextto,”ismore
common.
• She sat beside (=nextto) himduringdinner.
• I like tositbeside myfriend.
(Mairs s.f.)
Bibliography:
Mairs, Jane. Meriab Webster. s.f.http://www.learnersdictionary.com/qa/difference-between-beside-
and-besides-preposition-adverb(últimoacceso:14de Enerode 2016).
talkenglish.com. s.f.http://es.talkenglish.com/grammar/prepositions-with-over-by.aspx(último
acceso:14 de enerode 2016).