Generally speaking, a particle is a word that doesn’t belong to the usual classes of words like noun, verb, pronoun, etc.
Authorities disagree as to which words to call “particles,” but most agree that the to of an infinitive and the words that look like adverbs or prepositions in a phrasal verb are particles. Compare:
The family traveled to Paris. (preposition governing the noun Paris.)
Now they are ready to go home. (particle, part of the infinitive “to go.”)
Jack and Jill went up the hill. (preposition governing hill)
Mr. Abrams will set up the conference room for the next meeting. (particle, part of the phrasal verb “set up.”)
The particle most likely to cause difficulty for the non-native speaker is the “adverbial particle” used to create a phrasal verb.
A phrasal verb is “a fixed combination of verb and adverbial particle” used in many colloquial and idiomatic expressions.
Phrasal verbs present difficulties for non-native speakers because their meaning is difficult or impossible to guess from the individual words that make them up. For example:
His son said that he was ready to turn in.
Where were you when the meeting broke up?
Some phrasal verbs have different meanings, according to context. For example:
He put out the light and went to bed. (“extinguish” in the sense of interrupting an electric current)
The firemen put out the fire. (“extinguish” in the sense of smothering flames)
Don’t forget to put out the cat before you leave the house. (“place outside”)
The heat caused the girl to pass out. (faint)
The lecturer asked me to pass out the papers. (distribute)
Turn up the radio so I can hear it. (increase the volume)
I didn’t expect you to turn up here. (appear)
Her behavior this morning doesn’t add up. (make sense)
She waits until she gets home to add up her tips. (count)
He’s likely to break down on the witness stand. (become emotionally upset)
The CEO asked the accountant to break down the quarterly figures. (analyze)
Be sure to fill in every blank on the second page. (complete)
The boss asked me to fill in for her at the summit meeting. (substitute)
Sometimes the particle is separated from the verb by another word:
He took his boots off before entering the house. (removed)
They called the doctor in when the child’s fever increased. (summoned)
Writers targeting non-native speakers may want to pay special attention to phrasal verbs when revising, either to replace a phrasal verb with a simple one-word substitute or to avoid using the same phrasal verb with different meanings in the same document.
Phrasal verbs easily replaced by one word
throw away: discard
send back: return
pull through: recover
put off: postpone
call off: cancel
cut down on: reduce
put up with: tolerate