These words are pretty similar and have only subtle differences and in spoken language many people might not be careful enough to use each of the words correctly. However I think the explanation from Longman Activator Thesaurus is quite helpful:
purpose: what you want to achieve when you do something; the reason you do or plan something, and the thing you want to achieve
when you do it:
The games have an educational purpose.
aim: something you hope to achieve by doing something:
The main aim of the plan was to provide employment for local people.
goal: something important that you hope to achieve in the future, even though it may take a long time:
The country can still achieve its goal of reducing poverty by a third.
target: the exact result that a person or organization intends to achieve by doing something, often the amount of money they want to get; a particular amount or total that you want to achieve:
The company is on track to meet its target of increasing profits by 10%.
objective: the specific thing that you are trying to achieve - used especially about things that have been officially discussed and
agreed upon in business, politics, etc. and agreed upon in business,
politics, etc.:
Their main objective is to halt the flow of drugs. | We met to set the business objectives for the coming year.
ambition: something that you very much want to achieve in your future career:
Her ambition was to go to law school and become an attorney. | Earlier this year, he achieved his ambition of competing in the Olympic Games.
Best Answer
As defined from the NOAD, grammar is, "the whole system and structure of a language or of languages in general, usually taken as consisting of syntax and morphology (including inflections) and sometimes also phonology and semantics."
It includes the syntax, but it's not limited to that.
The syntax of a language is, "the arrangement of words and phrases to create well-formed sentences in a language."
For example, the syntax is about which order subject, verb, and object have in a sentence to form a well-formed sentence. A sentence like "like it I" is not considered a well-formed sentence, basing on the English syntax, even if people would understand that the correct sentence is "I like it."