Perfect Tense

                                                               Present perfect 
Affirmative
s.sub.+has+v3rd form+o.                                                                 He has written a letter.
p.sub.+have+v3rd form+o.                                                               We have written letters
Negative
s.sub.+has+not+v3rd form+o.                                                           He has not written a letter.
p.sub.+have+not+v3rd form+o.                                                        We have not written letters.
Interrogative
Has+s.sub.+v3rd form+o.+?                                                             Has he written a letter?
Have+p.sub.+v3rd form+o.+?                                                           Have we written letters?
Double Interrogative
Q.w.+has+s.sub.+v3rd form+o.+?                                                   Why has he written a letter?
Q.w.+have+p.sub.+v3rd form+o.+?                                                 When have we written a letter?

                                                                          Past perfect
Affirmative
s.sub.+had+v3rd form+o.                                                                 He had written a letter.
p.sub.+had+v3rd form+o.                                                               We had written letters
Negative
s.sub.+had+not+v3rd form+o.                                                           He had not written a letter.
p.sub.+had+not+v3rd form+o.                                                        We had not written letters.
Interrogative
Had+s.sub.+v3rd form+o.+?                                                             Had he written a letter?
Had+p.sub.+v3rd form+o.+?                                                           Had we written letters?
Double Interrogative
Q.w.+had+s.sub.+v3rd form+o.+?                                                   Why had he written a letter?
Q.w.+had+p.sub.+v3rd form+o.+?                                                 When had we written a letter?

                                                                          Future perfect
Affirmative
s.sub.+will/shall+have+v3rd form+o.                                           He will have written a letter.
p.sub.+will/shall+have+v3rd form+o.                                            We shall have written letter
Negative
s.sub.+will/shall+not+have+v3rd form+o.                                     He will not have written a letter.
p.sub.+will/shall+not+have+v3rd form+o.                                     We shall not have written letters.
Interrogative
Will/shall+s.sub.+have+v3rd form+o.+?                                       Will he have written a letter?
Will/shall+p.sub.+have+v3rd form+o.+?                                       Shall we have written letters?
Double Interrogative
Q.w.+will/shall+s.sub.+have+v3rd form+o.+?                              Why will he have written a letter?
Q.w.+will/shall+p.sub.+have+v3rd form+o.+?                              When shall we have written  letters?