The Conditional

She would often find herself at the library, and would browse through the fiction section, padding softly along the rug while her finger slid over the spines of dusty books.

Use of the helping verb "would" with another verb forms the conditional tense. The conditional is used to describe habitual or recurring actions, as well as potential actions or the hypothetical. For example, if you ask someone a "What if?" question, the proper answer should be in the conditional -- "If terrorists attacked my school, I would probably experience a panic attack."

When to not use the conditional:

• Describing what is about to happen. (After she stepped through, he would open the door and would beckon her to step to the security desk.)
• Describing what did happen, at one specific point in time. (He would lift his weapon and after Jason screamed, he shot him point blank.)
• Describing what is happening in the immediate present. (She would give him a flirting smile, sitting on the bench beside him. Kara touches her hand on his arm and would lean forward, catching his eye.)

The Subjunctive

If I were to die at the hands of terrorists, and the murderer were apprehended, I do not know how my family would react.

The subjunctive indicates a hypothetical state (like the conditional) but is only used in a dependent clause (or a clause that cannot form a sentence on its own.) According to Wikipedia, it may express "states of irreality such as wish, emotion, possibility, judgment, opinion, necessity, or action that has not yet occurred." It is not commonly used in written or spoken English, but ought to be used in proper written English outside of dialogue. A more complete explanation of the present and past subjunctive moods as opposed to the normal indicative mood, can be found in chart form in the linked reference at the bottom of this page.

Lingering Prepositions
Shoot 'em up dead!

Lingering prepositions occur when a preposition appears at the end of a phrase or clause.

Examples:
When can you drop off the kids at school?
She was the most courageous woman that I knew of.
If they refuse to give up, we'll be forced to go in.
The only direction you can go is up.
What will the exam be on?

I have only this to say -- never do it in any kind of formal writing. In colloquial speech, it is accepted and widely used, but in written materials, it creates the perception of an inability to write well or to choose strong verbs and sentence structures.

Here are each of the previous sentences with better phrasing:
When can you bring the kids to school?
She was the most courageous woman of whom I knew.
If they refuse to surrender, we'll be forced to breach.
Up is the only direction in which you can go.
What will the exam cover?

---

See Subjunctive Mood, retrieved from Wikipedia, 11 Oct. 2011.

To be frank, some of the "solutions" to the lingering prepositions that you provided sound much worse than their supposedly incorrect counterparts, in particular "She was the most courageous woman of whom I knew" and "Up is the only direction in which you can go." Using either of those in formal writing would actually draw attention to the sentence as being clunky and awkward, since the incorrect versions have arguably entered the lexicon as acceptable in formal writing as well. The incorrect versions definitely don't create the perception of an inability to write well; those versions may sometimes be more appropriate depending on the tone and style of the piece.

Agree with Pseudosyne's point: A rural child would likely not go around saying "I am the grammarian about whom your mother warned you." There are times where incorrect grammar can make a more powerful statement than technically correct constructions.

Also on the subject of the subjunctive: It actually appears more often than we might think. In the famous R.I.P. inscription on headstones, the letters stand for the Latin phrase requiescat in pace. Literally translated, it reads "May he/she rest in peace." That "may" is the subjunctive mood at work.

No, I fully believe that dialogue should not conform necessarily to accepted grammatical standards. I am referring to prose, narrative, and formal writing, rather than writing inside of quotes marks -- what people are saying, that is to say.

Even then -- the voice of your writing should reflect the character and the message you want to convey. It's not about grammatical perfection, but rather using those words to convey the message, tone and emotions you want the reader to experience. If you slavishly commit to grammar as such that you're writing such technical sentences that, while correct, read like a stereo manual, it's going to ruin any effect the post might have otherwise had.

From an editor's perspective the power of word choice is the power of the composer to inflict their voice upon the reader. What Ylanne is presenting here in this thread with lingering prepositions is not precisely a question of Correct Versus Incorrect. It is an option between Good Versus Better. Personally, I believe that Ylanne's adherence to sound sentence structure is among the best advice to give to those who are inexperienced or struggling. The prose composers who know what they are doing will do what they want regardless of rules or established decorum.

Thanks go to Ylanne for assembling this brief guide. Cheers.