The following words can be changed into new ones according to a certain pattern. What change has to be made, and what are the new words?

VISOR
WHEN
AGATE
CELERY
SUBTLE 
COMPOSE

Answers:

The letters (word) IT can be inserted somewhere in each of these words to make a new word:

VISITOR
WHITEN
AGITATE
CELERITY
SUBTITLE
COMPOSITE

Note: Other possible words: POLE-POLITE, BRAIN-BRITAIN, GRAVY-GRAVITY, BURRO-BURRITO
In its original form, this puzzle was reversed - dropping IT from the longer words.

Credit:
Will Shortz
The Puzzlemaster Presents Vol.2
LOSING IT