I need help here:

[edwardhyde22]

Ok guys,

This is reallty getting me,
In english you have root words like...

Medic
Science
Politics

and then... these words get extended to form words like:

Medical
Scientific
Political

What rule is it in english grammar that applies such word extensions??
I need to do something similar, but i have no rules i can compare to because i have no idea what im looking for.

Thanks in advance!

[QuantumWraith]

I believe this is the page you're looking for?:

http://en.wikipedia.org/wiki/Noun_adjunct

[Trailsend]

More generally, it sounds like you're wondering about derivational morphology. English has tons of different derivational rules—some of them change words from one word class to another while transforming their meaning in various ways, others alter their meaning within the same word class.

Some familiar examples:

(noun) + al => adjective, "pertaining to (noun)"

Nation => National. "The nation's flag is a symbol of national pride."
Medicine => Medicinal. "She makes the medicine from herbs with medicinal properties"
Music => Musical. "I love music, but I have no musical talent."

ex + (noun) => noun,, "something which was previously a (noun)"

Mayor => ex-mayor
Convict => ex-convict
(Girl|boy)friend => ex-(girl|boy)friend

(verb) + er => noun, "some(one|thing) that (verb)s"

Teach => Teacher
Interview => Interviewer
Employ => Employer

(verb) + ee => noun, "some(one|thing) that is (verb)ed"

Interview => Interviewee
Employ => Employee


So, there isn't a rule in English that applies these kinds of extensions...there's bajillions of them.