Is there any major difference the comma makes in: "I bought a pen[,] looking good"

Question

I have been trying to understand the actual construction of these type of sentences, but there still is a confusion to my understanding. I have seen many answers to questions regarding this type of sentence, but I'm still stuck.

[1]I bought a pen, looking good.

[2]I bought a pen looking good.

In [1] there is a comma but in [2] there isn't any comma. Is there any major difference between [1]and [2]?I think the sentence is a shortened form of :

I bought a pen that was looking good.

But what about [2]? Is it shortened?

[3]I saw him running.

Is [3] shortened form of :

I saw him who was running. I thought of this because I am confused about why suddenly a participle form comes after a noun or pronoun.

In [3] 'saw' is a verb of perception. What if it is a different type of verb.

Are those sentences a shortened form of another sentence? Why did the participle come suddenly?

Please give me a proper explanation.

Answer 1

Beginning with your third example, the sentence structure has the SVO structure.

SVO stands for Subject + Verb + Object. This is a very common sentence structure in English.
Subject = "I" Verb = "saw" object = "him"

In this case, the participle running modifies the object, him. It would be possible to modify the object further with prepositional phrases, or the participle could be modified with adverbs. For example:

Example [3] modified with a prepositional phrase:

I saw him running down the street.

Example [3] modified with a prepositional phrase and an adverb:

I saw him hurriedly running down the street.

The adverb could be placed at the end of the preposition depending on what you wanted to emphasize. Such as:

I saw him running, down the street, hurriedly.

The type of verb modifying the main subject would not effect the object's participle.

For example, the following sentences are all also correct:

I see him running.

I will see him running.

I did see him running.

I intend to see him running.

The first two examples in the query seem more ambiguous in their meaning, and border on nonsensical. They would be better understood in context, and colloquially they would not necessarily be considered incorrect. Again, the example sentences have the SVO construction. Normally, in English, the adjectives come before the nouns.

Alternatively, a more standard way would be as follows:

I bought a good looking pen.

I bought a good pen.

I bought an attractive pen.

In the first example given, perhaps if the "looking good" modified the subject this would make more sense, but it would, in this case, be written like this:

I, bought a pen, looking good.

The commas more clearly show that "looking good" modifies the subject, "I".

or the construction could be altered for more clarity as follows.

I, looking good, bought a pen.

In the second example, without the commons. The presumed longer form, "I bought a pen that was looking good." is more correct.

Answer 2

Neither of the pen sentences has an obvious meaning out of context. I would not utter those words, with or without comma, if the sense I wanted to convey was I bought a pen that was looking good. I might say "I bought a pen that looked good," but more likely I would say "I bought an attractive pen" or maybe "I bought a good-looking pen."

"I saw him who was running" is not something you would commonly hear a native speaker say. It's more of a logically similar statement than a longer version of *I saw him running." It is not even precisely equivalent; the clause gives the longer sentence a slightly different function.

I saw him running requires "him" to have an antecedent, and it describes the activity he was doing when the speaker saw him. On the other hand, I saw him who was running both indicates that the speaker saw someone and identifies the person seen as the running person.