Some prepositions also function as an adverb.

How to distinguish them properly?

please Explain it to me if there are some rules.

All of the prepositions that we have been seeing in phrasal verbs are functioning as adverbs, Hanuman.

Rule 1 (but I think we have reviewed these before):

I picked up the child / I picked the child up -- both OK, therefore a phrasal verb, and 'up' is an adverb.

I rowed up the river /X I rowed the river up -- the latter is no good; therefore 'up' is a preposition.

Or is this not what you mean? Perhaps another member has a clearer idea.
I was taught that how a word is used determines its part of speech.

A preposition is always part of a phrase, which itself can be used as a single part of speech.

In the expression "I'll be around," around is an adverb answering where.

In "He went around the corner," the prep. phrase 'around the corner' is used as an adverb also answering where.

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In addition to the fabulous information given so far, please note, every word in a sentence has a form (what it looks like) and a function (what it does). Let's look at "up", its form and function in this sentence:

1. We called him up.

Given the word order, we know right away that "up" is not a preposition in form. Here's why: Prepositions require an object. In our example, "up" sits alone, so it can't be a preposition. It's as simple as that. Prepositions require an object, and "up" doesn't have an object, so it must be an adverb:

1. We called him up. (adverb in form)

To determine a word's form, we look at how and where it sits the structure, and to determine its function, we ask one of the 5 W's (Who, What/noun; What kind/adjective; When, Where, How, Why/adverb).

Q: We called him how?
A: We called him up.

In short, "up" is an adverb in form, that's what it looks like, and it's an adverb in function. That's what it does.

1. We called him up. ("up" modifies "called", so it's an adverb in function)

Now let's look at "up" in this sentence:

2. We rowed up the river.

Right away, given the word order, we know that "up" doesn't sit alone, that it takes an object, notably "the river", which means it's a preposition in form:

2. We rowed up the river. (preposition in form)

Now let's determine its function:

Q: We rowed where?
A: We rowed up the river.

The entire phrase "up the river" functions as an adverb. "up" has no function of its own. It shares the function.

2. We rowed up the river. (adverbial phrase in function)

In cases where structurally ambiguity plays a role, such as, say,

A. Send up the tray.
B: Send the tray up.

the fact that there are two variants (A. & B.) helps us determine the function of "up". If "up" can be separated from the noun phrase "the tray", then it's not a preposition. Prepositions must occur at the head of their own phrase.

In short, every word has a form and a function, and the two don't always agree:

1. We called him up. (adverb in form)
1. We called him up. (adverb in function)

2. We rowed up the river. (preposition in form)
2. We rowed up the river. (adverbial phrase in function)

Note that, a long time ago, the telephone was mounted high up on the wall, and in order to use the phone, one had to step on a stool, pick up the receiver, and call "up" into the mouth piece. Today, phone styles have changed, and yet we still say "call up".

All the best,
Hello Casi!

Thanks for valueable information.

They ran round the tree.

"round the tree" prepositional phrase, Am I right?

So "round" here is preposition, right!

Yes. The word 'round' (informal for 'around') is a preposition with 'tree' its object. The whole phrase serves as an adverb.
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Yes. That's correct. But, and as the previous poster has noted, be more precise in your explanation. Try,

"round the tree" is a prepositional phrase in form, and it functions as an adverb.