Raymott commented that it is difficult to define a "complete thought." He is right, but I nonetheless think the "complete thought" criterion is an essential part of an independent clause and can help one determine whether a clause is independent.
Please consider the following six examples. The first three are from a law textbook authored by two Britons, the fourth one is from the European Court of Justice, and the last two from me. I have commented each of them and would appreciate some feedback.
Don't expect legal writing to have good punctuation or conventional punctuation.
1. "The correct legislative procedure in respect of a proposed piece of legislation is determined by the legal base of the proposed legislation, that is to say the Treaty Article which gives the Community power to act in that area."
I think the comma is correct. Sure, the clause starting with "that is to say" has a subject and verb, but something seems to be lacking. I cannot, however, express this in grammatical terms.
"That is to say" is an adverb; I would put a comma after it. The comma after "legislation" is right because it introduces an appositive.
2. "Article 3 does not however provide that the measures within its scope contravene Article 28 only 'where the restrictive effect of such measures on the free movement of goods exceeds the effects intrinsic to trade rules,' that is 'where the restrictive effects on the free movement of goods are out of proportion to their purpose' or where 'the same objective can be attained by other means which are less of a hindrance to trade.'"
This one I'm not as confident about, perhaps because the "that is" clause is so long. But if you were to isolate the clause from the rest of the sentence, I think you'd come to the conclusion that it can't stand on its own because of "where," which functions as a dependent word in the sentence. Or at least I believe it does.
Same as example 1.
3. "Member States must be able to establish not only that the measures in question are not protectionist but also that they are no more than is necessary to achieve the objective in view, in other words that they satisfy the principle of proportionality."
In this example the comma is probably wrong. "They satisfy the principle of proportionality" is an independent clause, one that isn't preceded by a dependent word (assuming that "that" isn't such a word).
Again.
4. "Individuals are therefore entitled to rely before national courts, against the State, on the provisions of a directive which appear, so far as their subject-matter is concerned, to be unconditional and sufficiently precise whenever the full application of the directive is not in fact secured, that is to say, not only where the directive has not been implemented or has been implemented incorrectly, but also where the national measures correctly implementing the directive are not being applied in such a way as to achieve the result sought by it."
What a monster of a sentence! Regrettably, such sentences often appear in the judgments of the European Court of Justice. Anyway, I think the comma after "secured" is correct because the clause that follows contains a dependent word.
Appositive, again.
5. "These developments have contributed to the 'juridification' of sport, that is to say, 'the process through which the general laws of the land penetrate the internal laws of sport.'”
I think the comma after "sport" is correct, but I can't really explain why, other than to say that the "that is to say" clause sounds incomplete.
One more time.
6. "It appears more probable, though, that rules justified on non-economic grounds are, in fact, rules justified on grounds of purely sporting interest, given the parallel the Court drew between non-economic reasons and purely sporting interest in paragraph 14 of Donà, namely, that 'reasons which are not of an economic nature ... are thus of sporting interest only.'”
The comma after "Donà" is probably wrong. But I'm not sure.
And yet again.
I'm sorry for making such a long post. Feel free to remedy any grammatical offenses I may have perpetrated in it.
Thanks a lot!
