Res Grammaticae

Or, things having to do with grammar (and writing in general).
Commas and their concomitants
A COMMA
  1. Separates main clauses joined by a coordinating conjunction (and, nor, but, or, for) and some short parallel clauses not joined by conjunctions.
  2. Sets off adverbial clauses or long adverbial phrases that precede or interrupt the main clause.
  3. Sets off transitional words and expressions (such as "on the contrary," "on the other hand"), conjunctive adverbs (such as "consequently," "furthermore," "however"), and expressions that introduce an illustration or example (such as "namely," "for example").
  4. Sets off contrasting and opposing expressions within sentences. I like ice cream, not cake. It costs 6500$, not 65$.
  5. Separates words, phrases, or clauses in series.
  6. Separates coordinate adjectives modifying a noun. A comma, however, is not used between two adjectives when the first modifies the combination of second adjective and the word or phrase it modifies.
  7. Sets off the parenthetical elements such as nonrestrictive clauses and phrases.
  8. Introduces a direct quotation, terminates a direct quotation that is neither a question nor an exclamation, and sets off split quotations. The comma is not used with quotations that are tightly integrated into the sentences in which they appear or those that do not represent actual dialogue.
  9. Sets off words in direct address, absolute phrases, and mild interjections.
  10. Separates a tag question from the rest of the sentence.
  11. Indicates the omission of a word or words used in parallel construction earlier in the sentence. When the meaning is quite clear, the comma can be omitted.
  12. Is used to avoid ambiguity that might arise from adjacent words.
Semi-Colons: happy ;) and sad ;( and avuncular =):-)
A Semi-colon
1. links independent clauses not joined by a conjunction. For instance: "Some people like nuts; others don't."
2. separates phrases in a series that contain commas. For example: "the computer, a Dell, and its printer; the dishes, including some fine china; and the dog bones"
Who and whom and this and that

Who and whom refer to people: that and which refer to animals and things (unless the animals have names).
This and that point to things. Generally, "this" points to something near or related to the speaker, and "that" refers to something near or related to the one spoken to. Generally, you should always ask yourself "is it absolutely clear what I am referring to?" whenever you use "this" or "that."

Precision and the sexes
Saying "Man is a rational animal, and they should use their rationality" is bad English, but if what you mean to say is that all humans are rational animals, it is also imprecise.
Ways to rewrite include:
Boldly to split or to split boldly? You have a choice:
In English, the infinitive comes in two forms: with "to" and without "to." For example, "try to do this" has "to do" as an infinitive, but "try doing this" has "doing" as an infinitive. When you have an infinitive with "to," it is considered correct style not to put anything between "to" and its verb. Doing so is called "splitting and infinitive," and will mark you as not knowing in the ways of style.

Traditionally wrong: I believe violence to essentially be evil.
Traditionally wrong, but it sounds so right: Our mission is to boldly go where no one has gone before.
Wrong for effect: I want to explain two things: how not to read and how to not read.
Practice:
He decided absolutely to never eat with his mouth open.
She tried to always be a loyal daughter.
She had to publicly apologize to the clown and to quickly go to the really ugly house of her too too hurtful aunt.
To badly err is all too human.
She, being a strange one, engaged secretly to solemnly promise to really try to happily eat broccoli.

However hopefully
However and hopefully are two words that should rarely begin sentences (note, however, that Merriam Webster's Collegiate Dictionary, 11th edn., allows "however" to begin sentences: it is a matter of style)
Sentences where "hopefully" means "full of hope" or where "however" means "to whatever degree" may have hopefully or however as their initial word.

When "however" means "but" or "on the other hand," however, it should never begin a sentence. There is no logical reason for that.

When "hopefully" means "I hope that," it should not begin a sentence. Again, there is no good logical reason for that rule. It is simply an oft-employed rule of style.

Your, you're, there, their, they're, to, too, two, then, than

Correct the following:
You're pants are on fire and your going to burn your #@$@#$ if you don't jump in the lake.
Your a genius, and you're shoes are pretty cool, to.
They're on there front porch drinking, and while their they're, there lighting you're pants on fire, while your sitting here.
To many people try two toot they're horns in tutus.
To many people, there is no difference between "then" and "than."
To gloves that were to red for there taste were on sale when she went too the store.

A potpourri farrago of relatively important stuff