How do I join more than one adjective together? I've seen "敦厚老实", where the two adjectives are simply put together, but I've also seen things like "x而x", "x又x" and "又x又x". 

What do these mean, are there any other ways， and which are the most common?

Thanks
(1.) In [(X) 而 (Y)] , "而" = "and" in English

Examples:

(快)而(準) = (quick) and (accurate)

(強)而(有力)=(strong) and (forceful)

(簡)而(清)= (simple) and (clear)

(2.) The [又(X)又(Y)] structure functions like [(X) and (Y)] in English, 

When (X) and (Y) are adjectives, the subject is being (X)and (Y) at the same time.

Examples: 

又(快)又(準) = (fast) and (accurate)

又(強)又(有力)=(strong) and (forceful)

又(簡單)又(清楚)= (simple) and (clear)

When (X) and (Y) are verbs, the two actions could happen at the same time or one following the other.

Example:

又(哭)又(笑) = (crying) and (laughing)

又(打)又(鬧) = (punching) and (yelling)

(3.) [(X)又(Y)] is just [又(X)(又)(Y) ] omitted the first 又

In this form, (X) and (Y) are usually two characters words. Since [(X) 而 (Y)] is similar but much more popular, [(X)又(Y)] is kind of redundant,  not many people would use it.


  I've seen "敦厚老实", where the two adjectives are simply put together


In this form, both adjectives have to be two characters words.

Example: 

快捷準確 (fast and accurate)

簡單清楚 (simple and clear)

強勁有力 (strong and forceful)

** You can use multiple four characters adjective clauses on one subject

Example:

他的演說 簡單清楚, 強勁有力 ( his speech is simple and clear, strong and forceful)