a lower vs the lower

[White Hat]

I need some help with the following sentence:

There are various grades of octane levels of gas. You will usually find such names as “Premium” or “Super” (the highest octane level) and “Regular” for the lower octane level.

The sentence is taken from a textbook for American English learners (written by a Russian author based on material taken from a native source). I need to know whether the use of the definite article is correct here.

In general, I'd love to check out a source that explains article use in terms of comparing two or more objects.

As far as the sentence above, I, for some reason, find that "a" would be more correct.

Please help me out! Thank you in advance!

 

[SoothingDave]

The grades of gasoline are quite definite. It is speaking of a specific, lower grade of gas.

(One can question that it should be the "lowest" octane if the comparison involves more than 2 grades of gas.)

 

[bhaisahab]

Yes. The definite article is correct.

 

[White Hat]

Yes, I got it now! Super!

 

[Ali Hsn]

Hello!

"Rule 6" on the website addressed below says that article "THE" can be used before comparative degree in case of choice. For example: "She is the weaker of the two sisters." Does it talk about the same thing occurred in the sentence Bennevis mentioned?

http://examsresult.org/when-to-use-definite-article-the-in-a-sentence

Thanks!

 

[White Hat]

Yes, that's a nice post. I think I've fully recalled this now. If we're talking about 3 or more objects, we'd say She is "the smartest of the three sisters". Otherwise, it has to be "She is the smarter of the two sisters". You may consider my post as an aside.