Let's talk about prepositional phrases.
So a prepositional phrase is a part of a
sentence that's not part of the core, so
it's not essential but it adds some
extra information. And if you look at
this sentence, we have three
prepositional phrases: we have "on toast,"
"with two slices," and "of bacon." So the
core part of the sentence then is "I like
my eggs." And you can see that has a
subject, "I," it has a verb, "like" (notice that
"like" can also be preposition at times),
and it has a direct object in "my eggs." So
we have a complete sentence there, and
then the rest of the sentence is
extra information. Now one of the key
things to realize about prepositional
phrases is that they always act either
as an adverb or as an adjective.
And in this
example we have two prepositional
phrases that act like an adverb, the
first two, and the last one acts like an
adjective.
So if you were to ask a question like,
"how?" or "where?",
then you can say, "well, I
like them
[where?] on toast [and how?] with two slices,"
which sounds a bit like a Dr. Seuss
story. But these questions are about
the verb, and if we're asking questions
about the verb, then we're typically
answering them with an adverb.
So an adverb modifies a verb, and as a
result, these prepositional phrases are
acting adverbially (I know that's quite
a mouthful). The
last phrase here, which is "of bacon," acts
like an adjective.
So we can call it adjectival if we want
to be technical. And in this case, what
we're modifying is the noun "slices." So if
we say, "what kind of slices?",
then we could say "well, of
bacon." So whenever we modify a noun, we
use an adjective. And as a result, the
prepositional phrase is acting like an
adjective.
So that's the first major thing to
recognize here--prepositional phrases
always consists of a preposition and an
object of the preposition, and, as a whole,
they work either as an adjective or an
adverb in the sentence.
The second thing to recognize is that
it's really easy to confuse prepositions
for conjunctions. So in these two
examples, we see, first of all, preposition
being used here. So "after the rain," "after"
is a preposition.
And together with "the rain," which is the
object of the preposition, all of this
together forms a prepositional phrase. So
there's our prepositional phrase, and that
adds some extra information to the main
clause. In the second example, "after" is a
conjunction, and we know that because "the
rain" no longer forms the object of the
preposition; instead, it's a subject
because it has a verb after it. So
together with "stopped," "the rain stopped,"
this becomes a clause.
So a clause is a subject and a verb
along with any other modifiers. Now, what
kind of clause is it? Well, the word "after," a
conjunction, makes it a dependent clause.
So dependent means that it cannot stand
by itself as a complete sentence but it
has to be tied to something else, which
is, in this case, "we went for a walk," which
is our independent clause. So be very
careful when you're thinking about
conjunctions and prepositions not to
confuse them for each other.
The very same word, in this case "after,"
can be a preposition or a conjunction. Of
course that doesn't apply to every
preposition, but there are a few that you
want to watch out for. So these are words
like "before" and "after" and even "because"
at times. So
be careful, look at the context, and the
context will tell you which one you're
dealing with. The last thing to realize
about prepositions is that they're not
supposed to come at the end of a
sentence. So that's a big no-no according
to some grammar books. Actually, I think
people are becoming more relaxed
about this final preposition. I'm okay
with it.
So you really have to decide for
yourself: are you are you fine with
having a sentence end on the preposition,
or do you want to move this somewhere
else in the sentence. So you could stick
at the beginning for instance: "by what
time do you need to be at the station at."
Well "at" is a preposition too so doesn't
work. But you can see the issue
that if you can rephrase it,
maybe it helps, but often it actually
sounds more natural to end on a
preposition. So I think this is one of
these tricky cases where, in a formal
context, I would probably try to avoid
ending on prepositions as much as I can,
but it may be inevitable at times, and I
think often it's not really a big deal.
So sometimes we have these rules in
grammar that exists for apparently no
purpose or reason, but you can
sort of take them or leave them, and this
is definitely one of those.