The sentence:
His music is not impossible to understand on the basic level for a Russian or French person.
About "for a Russian or French person", which does it modify, "the basic level" or "impossible"?
The phrase "for a Russian or French person" does not modify anything and is not part of any modifying element.
Modification is used to specify the characteristics of a "Thing". (Note that the word Thing refers to the functional element of the clause and not to the physical entity or entities designated by the specific nomenclature.)
For example, in the following (Imperative) clauses, the Thing is "books", which has been shown having undergone progressively more modification. This type of modification is known as Premodification (pre - before the "thing") and is done according to the conventional ordering of the various categories of Premodifier in English.
Give me the books!
Premodification of
books using the deictic
the
Give me the two books!
...using the deictic
the + the numerative
two
Give me the two red books!
...using the deictic
the + the numerative
two + the epithet
red
Give me the two red English books!
...using the deictic
the + the numerative
two + the epithet
red + the classifier
English
As can be seen above, Premodification results in expansion of the Nominal Group (
the books becomes
the two red English books).
A characteristic of English is that one can also
postmodify Nominal Groups. This is done by addition of an embedded clause from which "that" may or may not be ellipted.
For example, in the Clause Complex
Give me the two big red English books (that) I lent you yesterday!
the Embedded Clause
"(that) I lent you yesterday" postmodifies the Nominal Group
"the two red English books" (which of course also contains the already mentions predomifications).
(Why do we refer to this as an "Embedded Clause? - because the Verbal Group it contains has no relevance to any "action" or "event", and is concerned only with modification. This might be something that is very important for students to take note of. Compare the function of the Verbal Group (
lent) in the two clauses
I lent you books yesterday with
give me the books that I lent you yesterday. The first refers directly to an "action" or "event"; the second does not.)
I refer back to the original sentence:
His music is not impossible to understand on the basic level for a Russian or French person.
This is a single clause and involves an
A is B type construction (A Relational Attributive Clause - an R.A. Clause -for the pedantic such as myself). More meaning can be imbued into the clause by providing "circumstances" under which the proposition governed by the Verbal Group holds true. In this case, the Circumstances are
on the basic level and
for a Russian or French person.
That is
A (His music)
is
B ( not impossible to understand; B in this case also contains embedding
)
+ The Circumstances (on the basic level; for a Russian or French person).
Thus
for a Russian or French person and
on the basic level are functionally equivalent in the sentence, and give information about the Verbal Group
is.
(To check this try:
His music is - on the basic level, for a Russian or French person - not impossible to understand.
Here you can quite clearly see the role of the Circumstance(s), which is to provide information relating to the Verbal Group. Although this is probably more representative of spoken rather than written English, the functional relationships are clear.)
Another writer might prefer a structurally different approach. For example in the offering
His music is not impossible for a Russian or French person
to understand on the basic level.
there are two clauses.
1. His music is not impossible for a Russian or French person
Finite Independent R.A. (A is B) Clause
(The Circumstance
for a Russian or French Person gives information about the Verbal Group
is.
)
2. to understand on the basic level.
Nonfinite Clause
(The Circumstance
on the basic level gives information about the Verbal Group
to understand.
)
It's for the reader and/or writer to decide which particular arrangement renders the highest degree of clarity.
