PREPOSITIONS

Prepositions are words which begin prepositional phrases.

A prepositional phrase is a group of words containing a preposition, a noun or pronoun object of the preposition, and any modifiers of the object.

A preposition sits in front of (is “pre-positioned” before) its object.
The following words are the most commonly used prepositions:

about	below	excepting	off	toward
above	beneath	for	on	under
across	beside(s)	from	onto	underneath
after	between	in	out	until
against	beyond	in front of	outside	up
along	but	inside	over	upon
among	by	in spite of	past	up to
around	concerning	instead of	regarding	with
at	despite	into	since	within
because of	down	like	through	without
before	during	near	throughout	with regard to
behind	except	of	to	with respect to

                                     

         
It is useful to locate prepositional phrases in sentences since any noun or pronoun within the prepositional phrase must be the preposition’s object and, therefore, cannot be misidentified as a verb’s direct object.

To the store is a prepositional phrase.
Store is the object of the preposition to, not the direct object of the verb drove.
           

Car is the direct object of the verb drove.
To the grocery store is a prepositional phrase.
           
NOTE:
A word that looks like a preposition but is actually part of a verb is called a particle.

Held up is a verb meaning “to rob.”
Therefore, up is not a preposition, and bank is not the object of a preposition.
Instead, bank is the direct object of the verb held up.

To avoid confusing prepositions with particles, test by moving the word (up) and words following it to the front of the sentence:
                Up the bank four armed men held.
If the resulting sentence does not make sense, then the word belongs with the verb and is a particle, not a preposition.
Note the difference:

The resulting sentence makes sense.  Therefore, up is a preposition.

The resulting sentence does not make sense.  Therefore, up is a particle in this sentence. 
    
The following examples illustrate the difference between prepositions and particles: