Adjective suffixes
Does anyone know how to choose a correct suffex for an adjective?

For instance: we have a noun "danger". Why do we say danger+ous but not dangerAL or dangerFUL etc.
Or why "friendly" but not friendOUS, friendFUL etc.

So what rules do we follow when we make adjectives from nouns or verbs??

Thank you in advance

Question

Adjective suffixes
Does anyone know how to choose a correct suffex for an adjective?

For instance: we have a noun "danger". Why do we say danger+ous  but not dangerAL or dangerFUL etc. 
Or why "friendly" but not friendOUS, friendFUL etc.

So what rules do we follow when we make adjectives from nouns or verbs??

Thank you in advance

Answer

There are course book exercises you can do on this, and they will help you to notice patterns.  English has many linguistic roots - French, Norse, Latin, Anglo-Saxon. All of them have contributed adjectives, and so there is no system of rules to learn which you can then use to predict accurately the correct suffix.  Keep reading and noticing patterns but don't try to look for absolute rules.