Syntax:

Syntax provides the structure and how to formulate the phrase or sentence w.r.t grammar of the language. It tells us about which composition is allowed from the character set of the language.   Each sentence must be a well formed sentence according to the grammar of the language. The grammar is expressed in a Number of rules that will be finite and these allow the formulation of any number of sentences. A language is defined in the form a quadruplet L(T,N,P,S) where T is set of terminals, N is a set of non terminals, P is set of productions or rules and S is the start symbol. For any language we must have an alphabet/character set, operators and rules. To form a grammar w.r.t a language rules need to be formed.  The basic structure of rule is LHS and RHS with some set of terminal and non terminal symbol. 

Syntax comprises grammar and vocabulary whereas syntactic analysis is known as parsing.  Semantics provides the meaning for the formulated /composed phrase or word or sentence. Semantic function can be incorporated inside the logic of a compiler or interpreter which evaluates ordering of statements for execution.