The goal of forward guidance is to steer market, as well as public, expectations about the future path of monetary policy. It would appear, to those without PhD.s that central banks are drifting from actions to words and the following chart shows the devolution over the past 20 years of central-banker-speak. We have come quite a way from the "never explain, never excuse" view of Montagu Norman in the early 20th century to the hope-laden promises of increasingly wordy statements today...
(click image for massive legible version)
and how the Big Four compare:
Source: Goldman Sachs