Conjunctions, Interjections

 - linking function

Coordinating Conjunction (coordinator)
 e.g. and, or, but
 - link units of equal syntactic status
 - two coordinated phrases form a new phrase of the same type as two constituent conjoins
 - syndetic coordination : involve an overt coordinator
 - asyndetic coordination : involve no overt coordinator

Subordinating Conjunction (subordinator)
 - introduce subordinate clauses
 - link units of unequal syntactic status
 - the string of words introduced by the subordinator is syntactically subordinate to what precedes it

 - expressions of emotion, physical state, agreement, disagreement, etc.
e.g. ah, erh, no, oh, ouch, yes, shit, etc.