These verbs may all express the act of breaking in on flow of words in order to make an addition, alteration or comment. To insert a letter, word or group of words is simply to put it in, often where it has a perfect right to be. Specifically, insert suggests that a space must be made in written or printed matter so that the addition may be fitted in: to insert an ad in newspaper. A caret [ [ ] marks the spot where an omitted word or letter is to be inserted in a line. To interpolate a word, passage or comment is to insert it where it does not belong – among words written or spoken by and attributed to another. Interpolations such as editorial comments, explanations and helpful emendations are permissible if enclosed in square brackets, as in: "The plot was obviously inspired by [Molière’s] Les preciéuses ridicules, one reviewer wrote." Interpolations that are not permissible are additions made by other hands that are passed off as part of the author’s original, for such interpolated matter corrupts the original text. To introduce something into a speech or piece of writing is to bring it in not only as an added part, or insertion, but as a new part, a change from what is already there.

• He was told that his speech would be more effective if he introduced examples to illustrate his points; After Shakespeare’s death, lesser playwrights introduced changes into his plays, interpolating spurious passages, stage directions, spectacle and music.

Both interject and the more formal interpose may mean to introduce abruptly. These words, however, are specifically used of oral comments that break in suddenly upon an otherwise even flow of speech. What is interjected is simply thrown in unexpectedly and forcefully, as an exclamation arising from a natural reaction.

• When that politician’s name was mentioned, the doctor interjected an oath into the conversation.

What is interposed is put in as a deliberate interruption, such as a protest or digression, and is meant to halt the speech or argument going on.

• A student interrupted the lecturer, ostensibly to ask a question, but actually to interpose his own opinion; When the witness began to shout angrily at his cross-examiner, the judge interposed a stern rebuke.