Sentence: a group of words that follow a grammatical structure in order to express an idea.

There are four kinds of sentence structures: 

1. Simple.
2. Compound.
3. Complex.
4. Compound-complex.

In addition, there are four kinds of sentence purposes:

1. Declarative. 
2. Imperative.
3. Interrogative.
4. Exclamatory.

The basic unit of sentence composition is the clause, and clauses come in two forms: independent and subordinate.

• An independent clause is a sentence with a subject and a verb that expresses a complete idea. 
  • John drove to the store. 
• A subordinate clause is a group of words that needs to be attached to an independent clause in order to complete its idea. 
  • After waking up late, John drove to the store.

In the first example above, we see the subject (John), the verb (drove) and the complete action (shown by the prepositional phrase "to the store). 

In the second example above, we see the subordinate clause "After waking up." On its own, that clause is incomplete because there is not subject, and the gerund form of the verb "to wake" does not indicated a complete action. But when it is attached to the independent clause "John went to the store," its action and meaning are clear and complete. This is the way we build sentences in our writing. 

Paragraph: a collection of sentences; the basic unit of writing composition.

Every paragraph should support and explain the thesis, or main point, of the writing. And paragraphs must have an organization that forwards this goal. Paragraphs should also only express one idea at a time.

For example, if you were writing a paper on how climate change has affected the winter sports industry in Vermont, you might have a paragraph that discusses how local innkeepers have seen their winter lodging reservations shorten at both ends of the winter sports season. So you would put things into that paragraph that support and illustrate the topic of innkeepers and a shortened winter season: a quote from an innkeeper, some statistics to support the idea, an anecdote from your observations about innkeeping in the winter, etc. But you would not put into that paragraph information about how restaurants are dealing with the shortening of the winter season. That would be a separate paragraph.

Paragraphs should all have these elements:  

• Unity: The entire paragraph should concern itself with only one purpose. 
• Topic Sentence: The central idea of the paragraph should appear in a topic sentence at or near the beginning of the paragraph. 
• Coherence: This is achieved by using logical bridges (having the same idea repeated in sentences) and verbal bridges (using keywords and transitions to create a thread within the writing).  
• Adequate Development: Use details, examples, quotes, statistics and other information to develop your paragraphs. And think of paragraphs as telling brief, illustrative stories about their topic. Conceiving of paragraphs and stories will mean they must have a beginning with a thesis (the topic sentence), a middle, with information that develops the idea or topic, and an end, where the writer analyzes the information and places it into the context of the writing itself. 

Transition: how sentences or paragraphs are put together.

Transition words and phrases are used to relate ideas. Writers may use transitions within paragraphs or between paragraphs so that ideas flow smoothly between sentences and between paragraphs. The following table provides some common transitions and how they are used.