A comma splice is the use of a comma to join (splice) two independent clauses, where the clauses are not connected by a coordinating conjunction such as "and". For example:
It is nearly half past five, we cannot reach town before dark.
Comma splices are generally considered errors in English, although they are acceptable in some languages, including French and German, and compulsory in others, including Russian and Ukrainian.
The prescriptive view
Comma splices are condemned in The Elements of Style, a popular American English style guide by E.B. White and William Strunk, Jr.
According to Joanne Buckley, writers often use conjunctive adverbs to separate two independent clauses instead of using a coordinating conjunction and, in doing so, create comma splices. A coordinating conjunction is one of the following seven words: for, and, nor, but, or, yet, so. A conjunctive adverb, on the other hand, is a word like furthermore, however, moreover. However, a conjunctive adverb and a comma or a conjunctive adverb between two commas is not strong enough to separate two independent clauses and creates a comma splice. Only semicolons and periods are strong enough to separate two independent clauses without a conjunction.
Grammarians disagree as to whether a comma splice also constitutes a run-on sentence. Some define run-on sentences to include comma splices, but others limit the term to strictly mean those in which independent clauses are joined without any punctuation, thereby excluding comma splices.
Strunk & White note that splices are sometimes acceptable when the clauses are short and alike in form, such as:
The gate swung apart, the bridge fell, the portcullis was drawn up.
Fowler (third edition, 1996) notes a number of examples by reputable authors:
We are all accustomed to the ... conjoined sentences that turn up from children or from our less accurate friends... Curiously, this habit of writing comma-joined sentences is not uncommon in both older and present-day fiction. Modern examples: I have the bed still, it is in every way suitable for the old house where I live now (E. Jolley); Marcus ... was of course already quite a famous man, Ludens had even heard of him from friends at Cambridge (I. Murdoch).
The comma splice is often considered acceptable in poetic writing. The editors of the Jerusalem Bible translate Isaiah 11:4 as:
His word is a rock that strikes the ruthless, his sentences bring death to the wicked.
Lynne Truss observes: "so many highly respected writers observe the splice comma that a rather unfair rule emerges on this one: only do it if you're famous." She cites Samuel Beckett, E. M. Forster, and Somerset Maugham. "Done knowingly by an established writer, the comma splice is effective, poetic, dashing. Done equally knowingly by people who are not published writers, it can look weak or presumptuous. Done ignorantly by ignorant people, it is awful."
Comma splices are also acceptable in passages of spoken (or interior) dialogue. In fact, this is often preferred in some instances over more correct usage as it emulates spoken speech more closely.
Simply removing the comma does not correct the error, but results in a run-on sentence. There are several ways to correct this:
Change the comma to another punctuation mark:
It is nearly half past five; we cannot reach town before dark.
It is nearly half past five – we cannot reach town before dark.
Write the two clauses as two separate sentences:
It is nearly half past five. We cannot reach town before dark.
Insert a coordinating conjunction following the comma:
It is nearly half past five, and we cannot reach town before dark.
It is nearly half past five, so we cannot reach town before dark.
Make one clause dependent on the other:
As it is nearly half past five, we cannot reach town before dark.
Because it is nearly half past five, we cannot reach town before dark.
Use a semicolon or dash and a conjunctive adverb:
It is nearly half past five; therefore, we cannot reach town before dark.
It is nearly half past five – therefore, we cannot reach town before dark.
LAY OR LIE
LAY – Lay takes an object.
Present Tense: We lay the papers on his desk every morning.
Past Tense: We laid the papers on his desk every morning.
LAID IS PAST TENSE OF LAY
LIE – Lie does not take an object. Means to recline, or be situated.
The papers lie on the desk until Mr. Smith arrives.
Past Tense: They lay there until his arrival.
LAY IS PAST TENSE OF LIE
LAY – is the verb, laid, laying, (vt). To cause to lie; deposit; especially, to place in a horizontal, reclining or low position. To place or arrange in a particular position. To put or place.
LIE – An untrue statement.
His statement was a lie.
LYING – To accuse someone of lying.
LIED – Verb
Always use them in dialogue, and use them most of the time elsewhere as well.
A restrictive clause is just part of a sentence that you can't get rid of because it specifically restricts some other part of the sentence. Here's an example:
Gems that sparkle often elicit forgiveness.
The words that sparkle restrict the kind of gems you're talking about. Without them, the meaning of the sentence would change. Without them, you'd be saying that all gems elicit forgiveness, not just the gems that sparkle. (And note that you don't need commas around the words that sparkle.)
A nonrestrictive clause is something that can be left off without changing the meaning of the sentence. You can think of a nonrestrictive clause as simply additional information. Here's an example:
Diamonds, which are expensive, often elicit forgiveness.
Alas, in Grammar Girl's world, diamonds are always expensive, so leaving out the words which are expensive doesn't change the meaning of the sentence. (Also note that the phrase is surrounded by commas. Nonrestrictive clauses are usually surrounded by, or preceded by, commas.) Here's another example:
There was an earthquake in China, which is bad news.
If you leave off the clause that says which is bad news, it doesn't change the meaning of the rest of the sentence.
A quick and dirty tip (with apologies to Wiccans and Hermione Granger) is to remember that you can throw out the “whiches” and no harm will be done. You use which in nonrestrictive clauses, and if you eliminate a nonrestrictive clause, the meaning of the remaining part of the sentence will be the same as it was before.
On the other hand, if it would change the meaning to throw out the clause, you need a that. Do all cars use hybrid technology? No. So you would say,
"Cars that have hybrid technology get great gas mileage."
Is every leaf green? No. So you would say,
"Leaves that are green contain chlorophyll.
It would change the meaning to throw out the clause in those examples, so you need a that. (Also note that the that clause isn't surrounded by commas. Restrictive clauses usually aren't set off by commas.)
Remembering to use that with restrictive clauses and which with nonrestrictive clauses is the best method, but the quick and dirty tip of using which when you could throw out the clause will also get you to the right answer most of the time.