The rule of thumb is consistency: consistency in person, number, tense, mood, voice, and tone within a sentence (or within a larger piece of discourse, like a paragraph or the piece as a whole).

PERSON: Is the subject of the sentence the person speaking (first person), the person spoken to (second person) or the person spoken about (third person)?

NUMBER: Is a person or thing singular or plural?
 

• Shifts in person: this occurs when, within a sentence, the person shifts from first to second person, from second to third person, etc. 
  Example: A person who is a nonsmoker can develop lung problems when you live with smokers. This shifts from third to second person.
  Revision: A person who is a nonsmoker can develop lung troubles when he or she lives with smokers. This is consistently third person. 
  Revision: If you are a nonsmoker you can develop lung troubles when you live with smokers. This is consistently second person.
• Shifts in number: this means shifting between singular and plural in one sentence.
  Example: They had the best time of their life. 
  Revision: They had the best time of their lives. 
  Example: All the candidates have a conservative record.
  Revision: All the candidates have conservative records.

1. A typical monastic community would usuallyconfine their dramatic activities to Christmas, Easter, and perhaps one or two saints' days.
2. Although we can locate a number of saints' plays in the early drama of Western Europe, you can't find them all located in one place.
3. Until the nineteenth century, comedy was inappropriate to serious religious dramas; they saw it as almost blasphemous.
4. The villainous characters in medieval drama are usually comic but not lovable; he is insensitive, even cruel.

• Shifts in tense, mood, voice.
• TENSE: when (past, present, future) the action of the verb occurs. Tense is marked by verb endings and auxiliary verbs (e.g., He walks home, He walked home, He will walk home, He was walking home.)
  Inconsistent: The road climbed up from the river bottom and the vegetation changes dramatically.
  Consistent: The road climbed up from the river bottom and the vegetation changed dramatically.
  The "historical present tense" refers to texts which may have written long ago but because they can still be read today are referred to in the present tense. 
  Inconsistent: In his article, Norman Frye criticized the postmoderns lack of ethics and asks whether literature should still teach as well as entertain.
  Consistent: In his article, Norman Frye criticizes the postmoderns lack of ethics and asks whether literature should still teach as well as entertain.
• MOOD: what the attitude of the speaker towards the action is
  Three moods:
• indicative: sentence presented as fact or straight assertion
• imperative: sentence presented as a command, often to an understood "you."
• subjunctive: sentence presented as doubtful or conditional
  Inconsistent: If he were more experienced, he will be able to help us. This shifts from subjunctive to indicative.
  Consistent: If he were more experienced, he would be able to help us. (Consistently subjunctive)
  
  
• VOICE: whether the agent or receiver of the action is in the subject slot (active vs. passive). A transitive verb, which transfers action from a subject to an object, can be expressed in active or passive voices. ("The door was opened" is passive, without an agent listed; "John opened the door" is active, with the agent in the subject slot.) Both voices are useful in writing, but shifting from one voice to another within a single sentence is very confusing. 
  Inconsistent: Columbus arrived in the New World, and it was believed he had found the coast of Asia. Shifts from active to passive.
  Consistent: Columbus arrived in the New World and believed he had found the coast of Asia. OR Columbus arrived in the New World; Spanish courtiers believed he had found the coast of Asia. OR Columbus arrived in the New World. It was believed by Spanish courtiers that he had found the coast of Asia.

WORKSHEET: Correct the shifts in tense, voice, and mood in these sentences:

1. Business has always been attracted by the language of football, for example, and it often will have invoked terms such as team player, game plan, and optioned out.
2. The connection is far from accidental in that both areas celebrated aggression.
3. If there were any doubt left about the connection between sports and business, recent surveys show that companies pay extravagant sums in order to rent private viewing suites at sports complexes.
4. Politicians will routinely use sports talk, and they use these figures of speech to curry favor with sprots-minded voters.
5. Politicians and businesspeople use sports analogies, and complex ethical issues are often transformed into simple matters of strategy.
6. Revise this sentence to eliminate sexist language: Any candidate should file his papers by noon.

Shifts in Tone: this is the speaker's attitude toward the subject or the audience, and it is derived from diction, verb selection, sentence structure, mood, voice, etc. Example: In his famous painting Persistence of Memory, Salvador Dali creates a haunting allegory for modern memory and time, a vision we just have to dub awesome.

WORKSHEET: Correct any shifts in these sentences so the sentences are consistent.

1. In contrast, can you think of someone who is so low-key that he's a couch potato, not very competititve, and easygoing in relations with others?
2. You now have in mind two homo sapiens who culd be descirbed as showing alpha and beta behavior
3. Alpha individuals get frazzled by stress more easily and tend ot suffer more coronary problems than betas.
4. Beta individuals have the patience of saints and perform well under high levels of stress and on tasks involving complex judgments and accuracy.

WORKSHEET: Change these direct quotations to indirect discourse

1. The great physicist Niels Bohr nailed a horseshoe on a wall in his cottage because "I understand it brings you luck whether you believe or not."
2. The mystery writer Agatha Christie believed that being married to an archaeologist was a stroke of good luck because as she got older "he shows more interest in me."
3. In a feverish letter from a battlefield in Italy, Napoleon wrote Josephine that he had received her letters and that "do you have any idea, darling, what you are doing, writing to me in those terms?"

A mixed construction means that a sentence begins with one grammatical pattern and then ends with another grammatical pattern. These incompatible sentence parts confuse readers.
 

• "The fact that" : this causes confusion when writers forget that this is actually a noun phrase acting as a subject or object. Example: The fact that design elements are as important to a play's success as actors. Here the writer thought the subject was "design elements" when it was really "the fact that".
  Revision: The fact that design elements are as important to a play's success as actors is often overlooked by students.
  Revision: Design elements are as important to a play's success as actors.
• Adverbial clauses: an adverb clause that begins with a subordinating conjunction (when, because, although) can't serve as a subject. Example: When a set is successful design pleases actors and theatergoers alike. Successful is serving as an adjective modifying design instead of acting as the last word of the adverbial phrase.
  Revision: When a set is successful, the design pleases actors and theatergoers alike.
  Revision: A successfully designed set pleases actors and theatergoers alike.
• Prepositional phrases: The object of a prepositional phrase, which is a noun, cannot function as the subject of a sentence. 
  Example: By creating a functional set design can help the audience believe the stage is a real place. "a functional set design is actually the end of the prepositional phrase but it is also being used as the subject of the sentence.
  Revised: Creating a functional set design helps the audience believe the stage is a real place. The whole phrase Creating a functional set design becomes the subject of the sentence; we've eliminated the prepositional phrase altogether.
  Revised: By creating a functional set design, the designer can help the audience believe the stage is a real place. The prepositional phrase remains discrete and an appropriate noun becomes the subject of the sentence.
• Maintain consistent relations between subjects and predicates (AKA faulty predication).
• This usually involves the verb "be". In the sentence "The child is happy," the verb "to be" is acting as a linking verb, basically saying the subject (the child) is equal to its complement (happy). If the subject and its complement don't match, we have a case of faulty predication. 
  Example: The resolving power of an electron microscope is keenly aware of life invisible to the human eye. A microscope's power cannot be keenly aware: people can be.
  Revision: The resolving power of an electron microscope helps us to be keenly aware of life invisible to the human eye.
  Revision: Aided by the resolving power of an electron microscope, we have grown keenly aware of life invisible to the human eye.
• Be careful of phrases beginning with when, if, or where when those phrases are acting as subject complements.
  Faulty: Electron illumination is if beams of electrons instead of light are used in a microscope.
  Faulty: Electron illumination is when beams of electrons instead of light are used in a microscope.
  Faulty: The reason electron microscopes have become essential to research is because their resolving power is roughly 500000 times greater than the power of the human eye.

WORKSHEET: Correct these sentences for mixed constructions

1. The fact that strays were overrunning the town and creating a health problem and nuisance.
2. When minute, pellet-sized bar codes became available and created a radical alternative to neutering or destroying strays.
3. With the bar code implants, runaway cats could be identified and quickly returned to pet owners instead of being destroyed.
4. One sign of trouble was when animal rights groups protested the indignity of the solution and when comedians asked, "Are people next?"
5. Advanced, miniaturized technology used for instant identification breathes fear into those who vigilantly protect against invasions of privacy.