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In an academic paper I'm using thus to indicate the conclusion of an argument. Today my professor said that thus should not be used in the beginning of a subordinate clause and suggested to use whence instead. Here's some examples to show how I use thus:

The substance did not freeze at normal pressure when the temperature dropped below 0 °C, thus it's not water.

Lisa's evidence does not satisfy the epistemic standard, thus she doesn't know that p.

Joel's utterance was offending, thus it was inappropriate.

Is it okay to start a subordinate clause with thus? Would using another word, e.g. whence, be more appropriate?

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It reads OK to me – Matt E. Эллен Oct 6 '11 at 13:38
@MattЭллен Would replacing 'thus' with any other word make it read better? – N.N. Oct 6 '11 at 13:40
You could try therefore or so, of those two I think therefore is the more formal sounding. I don't think you need to change from thus. – Matt E. Эллен Oct 6 '11 at 13:48
@MattЭллен Those are the three words (so, thus, therefore) keep iterating when writing arguments. So there's no other word that I can use (except for explicitly indicating conclusions)? I'm thinking of consequently. – N.N. Oct 6 '11 at 13:54
@cindi I'm sure. Yes, hence is a good candidate. I see that it's listed as an adverb though so I'd have to add an and before it to comply with what onomatomaniak says. – N.N. Oct 6 '11 at 14:39
up vote 11 down vote accepted

Neither thus nor therefore should be used as a conjunction to connect two independent clauses.

Thus, your example sentences are run-ons. You should use a semicolon to separate the clauses, like so:

I do not wish to offend the grammar gods; thus, I obey their arbitrary rules.

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Great example! So there's no way to do this without a semicolon? I feel that in most situations natural language should be able to do without it. – N.N. Oct 6 '11 at 14:02
Without a semicolon, thus would either start a sentence or occur somewhere within a single independent clause, often offset by commas. If you want to use it in a compound sentence, you still need a proper conjunction. Ex: "Henry was best at piano, and thus was he selected to play at the concert." – onomatomaniak Oct 6 '11 at 14:07
I wouldn't be afraid of semi-colons. Just learn the rules and use them correctly. But that's a different question. – Jay Oct 6 '11 at 14:19
Where does the rule come from? Looking at the use of these adverbs as conjunctions I see they are frequently separated by two commas rather than a semicolon and comma. – z7sg Ѫ Oct 6 '11 at 15:21
@z7sgѪ The rule is that a compound sentence requires a conjunction; "thus" is not a valid conjunction in these situations. Many people never learn this rule, and thus such words are commonly misused. This is okay: "She always came late, thus keeping the class waiting." This is not: "She always came late, thus she kept the class waiting." This is: "She always came late; thus, she kept the class waiting." – onomatomaniak Oct 6 '11 at 15:56

Thus is an adverb and so, for that matter, is therefore. As such it cannot introduce a subordinate clause. In any case, the words following thus in your examples do not constitute subordinate clauses. I would write the sentences (ahem) thus:

The substance did not freeze at normal pressure when the temperature dropped below 0 °C. We can therefore conclude it's not water.

Lisa's evidence does not satisfy the epistemic standard. That suggests that she doesn't know that p.

Joel's utterance was offending. That made it inappropriate.

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Thanks for your answer. Is there a shorter way to write the sentences? Dividing each example into two sentences and adding more words seems overly cumbersome. – N.N. Oct 6 '11 at 15:00
Short sentences are generally easier to read. Still, if you insist: 'The substance did not freeze at normal pressure when the temperature dropped below 0 °C, which leads us to conclude it's not water.' 'Lisa's evidence does not satisfy the epistemic standard, which suggests that she doesn't know that p.' 'Joel's utterance was offending and that made it inappropriate.' The words beginning with 'which’ in the first two sentences constitute subordinate clauses. The words following ‘and’ in the third are a coordinate clause. – Barrie England Oct 6 '11 at 17:26
Either of these suggestion makes the logical structure of the sentences less obvious. I'd prefer a construct where it's clear, though not verbose, what the premise is, where it's clear that the conclusion follows from the premise and where it's clear that the three sentences has similar logical structure. – N.N. Oct 6 '11 at 20:41

Your professor has it exactly backwards: replacing thus with whence in the examples you gave results in a sentence that is ungrammatical and incomprehensible. However, thus is not the best word for these examples. I find that all of them read better with therefore:

The substance did not freeze at normal pressure when the temperature dropped below 0 °C, therefore it's not water.

Lisa's evidence does not satisfy the epistemic standard, therefore she don't know that p.

Joel's utterance was offending, therefore his utterance is inappropriate.

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Why do you think it reads better with therefore? My preference for thus is that it's short so that it does better than therefore in places where you don't need to emphasize conclusions. – N.N. Oct 6 '11 at 13:50
@N.N., my preference for therefore is actually because it is longer and more emphatic. Thus works best for introducing obvious or intuitive consequences, while the longer, more strident therefore emphasizes the nature of a logical inference. – JSBձոգչ Oct 6 '11 at 13:59
None of your three examples is grammatically correct, at least not in standard American English. They all lack a conjunction. – onomatomaniak Oct 6 '11 at 17:01
Therefore is a conjunctive adverb. It connects ideas logically like a conjunction, but acts gramatically like an adverb. Two independant clauses joined by a conjuctive adverb must either be treated as two sentences or be joined with a semicolon. – Kevin Cathcart Oct 6 '11 at 21:24

This doesn't directly answer your question, but "whence" means "from where": it would be completely inappropriate in the examples you gave. Also, "whence" is an old word that is not really used in modern English. Correct usage of "whence" would be, for example, "Whence do you come, stranger?" It can be used non-literally for a reason rather than a place, like, "I had gotten the job Bob wanted, whence his efforts to sabatague me."

Onomatomaniak says that "thus" is not a conjunction. I always thought it was and have used it as such, but I see that at least one dictionary agrees with him and says it's an adverb. Thus, I guess you should begin a new sentence before writing "thus" or use a semi-colon.

All that said, if a teacher tells you to do X to pass his class, even if it's wrong, there's rarely anything to be gained by arguing about it. Like, if the teacher insists that 2+2=5, then on the test I would put 2+2=5, and once the class is over go back to doing it right. :-)

By the way, the second example you gave should say "she DOESN'T", not "she DON'T".

And in the third you probably shouldn't repeat "utterance". Better to say, "Joe's utterance was offensive, thus it was inappropriate."

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I've corrected the last two examples according to your comments. – N.N. Oct 6 '11 at 14:21
If most people use thus as a conjunction, then it is a conjunction? – N.N. Oct 6 '11 at 14:22
@NN: Ah, one of the fundamental questions of language. When someone says, "90% of English speakers think that the word 'x' means <such-and-such>, but they're all wrong, it really means <whatever>", I have to ask, if almost everyone agress that it means such-and-such, then pretty much by definition that's what it means, regardless of what some reference says. Language has no objective standard like physics. That leaves the question of whether it is true that "most people" use "thus" as a conjuction. I don't know. You can easily avoid the problem by writing "and thus" instead. – Jay Oct 7 '11 at 16:41

The question is nearly a year old as I post this, but a new answer is needed to correct an inaccuracy shared in one way or another by no fewer than three earlier answers, regarding the word whence.

It is true that whence, like hence and thence, is an adverb. However, very occasionally but nonetheless entirely properly, whence unlike hence and thence is alternately used as a conjunction. For example,

Cats hunt mice, whence they derive their cruelty.

Of course, my own usage bears poor authority, but what of Milton's?

This you might have learned out of the Third Book of his Annals, whence you have all your regal right.

The word means "from which place" or "from which fact," but so used the preposition "from" is omitted, whence the only part of speech one can impute to the word, so used, is the conjunctive. (How's that for awkwardly pretentious writing on my part? At any rate, the usage of whence in the very paragraph you are reading may serve to make the point.)

Here is a real, past sentence of my own in which the conjunction whence is less pretentious:

This is not because swapping is wrong, but rather because the inner sum after the swap diverges, whence the outer sum after the swap has no concrete summand on which to work.

Could I not have used so there? Yes, I could, but so does not mean quite the same. The conjunction so in that place would tend to connote what Aristotle calls "efficient causality," whereas I had Aristotle's "final causality" in mind, as seemingly did Milton, as (if you will excuse the expression) did the cat.

The last of the three quotes happens to show one of only two such uses of whence the computer finds in a 600-page manuscript, so it is hardly asserted that whence the conjunction were common! It is not common. However, it is licit, old, established, nonarchaic, Saxon, occasionally indispensable, and always sanctioned by good writers' use.

But, still, admittedly, I do not think that it fits your particular sentence well.

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Thus is used to indicate "as a result of", whereas whence means "from which or where." Starting a subordinate clause with thus is entirely appropriate, but using whence in the examples you provided would not be grammatically correct.

You may find your professor unwilling to accept anything other than his own reasoning, and if so I would look for another way to convey your thoughts.

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