I'm reading a book No Apparent Distress by Rachel Pearson and saw a comma between the following compound sentence "'I'm sorry, I don't cry as much." Why is there a comma instead of a semicolon? Is this not a comma splice?
As Bryan Garner observes:
…most usage authorities accept comma splices when 1) the clauses are short and closely related, (2) there is no danger of a miscue, and (3) the context is informal. Thus, “Jane likes him, I don’t.” But even when all three criteria are met, some readers are likely to object. And in any event, a dash or a semicolon seems preferable to a comma in a sentence like that one. — Bryan A. Garner, Garner’s Modern American Usage, 724.
Garner’s example is not particularly well chosen because it is a strong contrastive whose weight a comma might not bear. In that case, I would tend toward either a period or m-dash. “Most usage authorities,” however, are merely relaxing Strunk and White’s 1918 insistence not only on brevity, but strict parallel structure:
If the clauses are very short, and are alike in form, a comma is usually permissible:
Man proposes, God disposes.
The gate swung apart, the bridge fell, the portcullis was drawn up.
The real question is whether the comma splice rule really applies here. The truth of the matter is that the vast majority of writers — whether “I’m sorry” is behavorial chatter or a genuine expression of regret — treat the clause as an introductory element, much as one does an imperative:
“I'm sorry, did Fran talk to you?” — Emma Straub, The Vacationers: A Novel, 2014, 119.
Being polite people, the British do say sorry quite a lot.
I'm sorry, have you got the time?
I'm sorry, do you know where Turnpike Lane Tube station is? — BBC Learning English
Trust me, I'm not the only one out there with these kinds of experiences. — James Maloney, The Lord in the Fires, 2014.
“Don't worry, you can trust me, I'm a professional.” — Alexandra Adornetto, Heaven, 2012, 188.
'Stop the car, I want to talk to him!' — Iman Verjee, In Between Dreams, 2014, 353.
Now, I’m sure among the billions of words on the internet, someone locked into the definition of a comma splice has slapped a semicolon after “I’m sorry,” but I could only regard such a usage as a hypercorrection, that is, a valid grammar rule ill applied.
It certainly looks like a comma splice to me.
But comma splices, and other things not strictly grammatical, can be acceptable as literary devices.
Consider the following from Tami Hoag's Ashes To Ashes
Her past was like a bad movie playing over and over and over in her mind, always right there, ready to pull to the surface emotions better left buried deep. Hate and love, violent anger, violent need. Hate and love, hate and love, hateandlove—all one word for her. Feelings so intertwined they were inseparable, like the tangled limbs of two animals attacking each other.
In particular, hate and love, violent anger, violent need is not a grammatical sentence. It's simply a list of nouns—and one without a concluding conjunction. But that doesn't matter in the context of the story. In fact, in terms of literary effect, it's more evocative than something grammatical might be.
The same is true of poetry and song lyrics.
The general term for this is poetic license.
From its entry in the Encyclopaedia Britannica:
Poetic license, the right assumed by poets to alter or invert standard syntax or depart from common diction or pronunciation to comply with the metrical or tonal requirements of their writing.
As a general rule, poetry has a carefully controlled verbal structure. The metre of the poem, the pattern of stressed and unstressed syllables, and the sounds and modulations of the words themselves all affect the subtle meanings and feelings that the poet may be trying to convey or evoke. Poets may distort normal prose patterns for the sake of form and therefore assume poetic license; it is solely a matter of aesthetic judgment and sensibility as to whether the alterations enhance or detract from the total effect of the poem.
While this entry only discusses poems, it also applies to fiction.
From Oxford Dictionaries:
The freedom to depart from the facts of a matter or from the conventional rules of language when speaking or writing in order to create an effect.
‘he used a little poetic licence to embroider a good tale’
Authors frequently use ungrammatical sentences. But the key to them doing so is that they use them deliberately rather than mistakenly.
Strictly speaking, your example sentence should be something like:
I'm sorry, but I don't cry as much.
I'm sorry; I don't cry as much.
I'm sorry—I don't cry as much.
I'm sorry. I don't cry as much.
Or even phrased without punctuation at all:
I'm sorry that I don't cry as much.
I'm sorry I don't cry as much.
But depending on the way the rest of the book is written, and the surrounding text, it may make more sense for it be written exactly as it is.