The precise meaning of comma splice

Question

I was told by one supporter that there is a case of comma splice in the following sentence:

When he was able to crack the Trident code, that was deemed by many as his major achievement in his cryptology career.

I've checked the definition of comma splice in the Wikipedia and read there that:

a comma splice or comma fault is the use of a comma to join two independent clauses

However, when I re-checked the sentence, I noticed that the first part of it (the one preceding the comma) is not an independent clause, but rather a dependent one because it starts with when.

Wikipedia gives a similar example of such dependent clause and lists it under the category "adverbial clause":

When he was in New York, he went to the Guggenheim Museum.

So, this is where I got confused. If the given sentence is consisted of a dependent clause and an independent clause, and a comma splice case is by definition a case of splicing two independent clauses, how can the given sentence then be a case of comma splice?

Answer 1

Your first example does not have a comma splice. Your "supporter" is wrong. This would be a comma splice.

He was able to crack the Trident code, many deemed this the major achievement of his deciphering career.

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Note: I repeat my suggestion (from my answer to your previous question) that "deciphering career" is awkward and likely not what you want to say. "Deciphering" is just something you do as part of the job. "Cryptography/Cryptology career"sounds better.

It's like saying,

his sauteing career

rather than,

his cooking career

or better,

his culinary career.

Yes, as a professional chef you might saute a hundred times a day -- but it's not what defines the job.

By the way, it's "cryptology" if you study the general theory and techniques for encrypting/decrypting communication, and "cryptography" if it's your job to regularly encrypt/decrypt communication. From the limited information in your sentence, I can't tell which would be more accurate.

Answer 2

While it's true that a comma splice is a comma that separates two independent clauses without a conjunction, the sentence in question could be considered a comma splice if the sentence is taken in context.

For instance:

"When was the crisis averted?"
"When he was able to crack the Trident code, that was deemed by many as his major achievement in his cryptology career."

In short, the first part of the reply has an elided independent clause:

^{The crisis was averted}When he was able to crack the Trident code, that was deemed by many as his major achievement in his cryptology career.

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In this context, the first clause is actually a missing independent clause followed its dependent clause.

If it were a piece of written dialogue, the comma would be incorrect. It should be replaced with a semicolon, or the second line broken into two sentences.

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To clarify, the dependent clause when he was able to crack the Trident code pairs with the missing independent clause here—not with the existing independent clause that follows the comma.

And to be explicit, these would be the methods of punctuating the full version:

✔ The crisis was averted when he was able to crack the Trident code; that was deemed by many as his major achievement in his cryptology career.

✔ The crisis was averted when he was able to crack the Trident code. That was deemed by many as his major achievement in his cryptology career.

✔ The crisis was averted when he was able to crack the Trident code—that was deemed by many as his major achievement in his cryptology career.

But not this:

✘ The crisis was averted when he was able to crack the Trident code, that was deemed by many as his major achievement in his cryptology career.