It is not always easy to discriminate between different parts of the sentence expressed by prepositional phrases.
The following parts of the sentence are apt to be confusing:
- a prepositional indirect object and an adverbial modifier;
- an attribute and an adverbial modifier.
#1. A prepositional indirect object and an adverbial modifier of place and manner.
Kate removed her eyes from the window and gazed directly at Papa. (Cronin)
Decimus had been born in Rome. (Douglas)
In the first example, the prepositional phrase at Papa is a pre; positional indirect object as the noun denotes a living being.
In the second example, the prepositional phrase in Rome is an adverbial modifier as the noun denotes an inanimate object and the question is: Where had he been born?
When the noun in the prepositional phrase denotes an inanimate object, very often two ways of analysis are possible.
His wife was sitting before a very little fire. (Galsworthy)
The prepositional phrase before a very little fire can be treated either as an adverbial modifier or an object.
#2. An attribute and an adverbial modifier of place.
I thought you were going to a party at the club. (Douglas)
The party will take place at the club.
In the first example at the club is an attribute as it modifies a noun. It answers the question: What party?
In the second sentence, the same prepositional phrase modifies a verbal group, consequently, it is an adverbial modifier of place.
These examples do not cover all the dubious cases in analysis, they only serve to show that there are many borderline cases.