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?
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
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
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.
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.
Shifting between direct and indirect discourse:
direct discourse is where you quote directly. Indirect discourse is
paraphrasing. When you move from one to another, there are verb changes which
must take place. Example: