I know that #1 is correct but #2 is not:

1. I was hungry so I ate the cake.
2. I was hungry therefore I ate the cake.

#2 should be written as:

3. I was hungry and therefore I ate the cake.
(or I was hungry; therefore I ate the cake.)

I also know that it's because "so" is a conjunction while "therefore" is an adverb.

My question is what determines a word to be a conjunction or an adverb. Apart from checking it up in the dictionary, do we have a logical way to tell?


Hello Ricky

No, unfortunately: there are no morphological features that distinguish one from another.

But if you read plenty of different kinds of English, from different sources, you'll acquire an ear for the usual distribution of common words.

Thanks, MrP.

According to the dictionary, "so" means "and for that reason; therefore". In other words, "so" and "therefore" are identical in meaning. If it's the case, I don't understand why they can be of different word types. For example, if I know that a word "xyz" means the same as "hungry", I'd expect "xyz" to be an adjective. Could anyone think of a "reason" for the difference, or know a way to tell if a word is a conjunction or an adverb? Thanks.

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My dictionary shows "so" as an adverb and as a conjunction.
It also shows "therefore" as an adverb and as a conjunction.

The example of "therefore" as an adverb is (coincidentally!):

Your information is inaccurate and your conclusion therefore wrong.

The example of "therefore" as a conjunction is:

I lost my money; therefore, I could not buy a ticket.

SO and THEREFORE are NOT the same although they can be used ALMOST (you'll see why) exchangeably in sentences such as:

"I woke up late so I missed the train".

"I woke up late. Therefore, I missed the train".

The meaning is exactly the same, except that THEREFORE is more formal (although THUS is even more formal but mostly used in writing) than SO (which is usually used in spoken English). When using THEREFORE in this context, always remember to use a PERIOD before the second clause (some people use a ";" as follows: "I woke up late; therefore I missed the train").

*SO can work as:

-ADVERB ("I was so angry")

-CONJUNCTION joinin to clauses ("I woke up late so I missed the train")

-ADJECTIVE ("say isn't so")

-NOUN ("so" as the fith note in a musical scale)

*THEREFORE works as:

-ADVERB ("I woke up late. Therefore, I missed the train"). NOTE: it's not a CONJUNCTION joining the two clauses! They're separate and have a meaning of their own (although funnily enough, they are kind of incomplete not gramatically but about the whole idea they are expressing, which seems incomplete if both clauses are separated... I know, crazy grammar). In this sentence, THEREFORE has a similar use to that of "naturally" -which works as an adverb- in the following sentece: "Naturally, we want you to come"

-Same meaning as THUS ("The buildings were made for soldiers. THUS they survived the war")

-Same meaning as CONSEQUENTLY, FOR THIS REASON, AS A RESULT in formal speech or writing ("Money market accounts are not insured, and THEREFORE/CONSEQUENTLY/AS A RESULT are considered more risky than passbook accounts"

Lastly, a Conjunction is different from an Adverb in that the former joins clauses, phrases or sentences while the latter modifies verbs ("he ran slowly"), adjectives ("it's very hot") or adverbs too ("he ran very fast").

Hope it helps!

Sal (ESL, EYL, EFL Teacher)
CalifJimI lost my money; therefore, I could not buy a ticket.
Please tell me if it is possible to put it this way : I lost my money, therefore, I could not buy a ticket. ('therefore' as conjunction)
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Thank you so muchEmotion: embarrassed