“Yes, we can.”

Three simple words. Uttered by a coach, a parent or a teacher they don’t amount to much. Spoken by Barack Obama they helped to catapult his candidacy for president. Words can have meaning, or they may be empty gestures, depending on who says them and in what context. That’s the point Robert Schlesinger makes in his new book, “White House Ghosts: Presidents and the Speechwriters.” Covering administrations from Franklin D. Roosevelt through George W. Bush, Schlesinger wants readers to understand how hard it is to both write and make speeches.

At a time when Obama has succeeded in claiming the Democratic nomination in part because of his soaring rhetoric, the timing of Schlesinger’s fine book could not be better. What the author makes clear is that great speeches are not accidents.

The presidents who worked most closely with their speechwriters are the ones considered the best communicators – Franklin D. Roosevelt, John F. Kennedy and Ronald Reagan. Not coincidentally, they are also the ones who spent the most time preparing before their major addresses.

But it is not just the effort that goes into the speech. The rhetoric also has to match reality. A journalist and Boston University professor, Schlesinger quotes Kennedy speechwriter Richard Goodwin as saying speeches can’t be measured simply by words.

Roosevelt’s “the only thing we have to fear is fear itself” would likely have been forgotten or ridiculed if the New Deal hadn’t followed. Kennedy’s “ask what you can do for your country” would have meant little if the Peace Corps hadn’t soon been created.

Conversely, President Bush’s “We believe that freedom can advance and change lives in the greater Middle East” rings hollow because people realize how little his administration has accomplished in Iraq and the rest of the region despite his swelling words.

Schlesinger writes that he began “White House Ghosts” with FDR because his was the first administration in the modern media age. “Roosevelt had a keen sense of public psychology and … insight that radio, the first live mass medium, lent itself to a previously unimagined oratorical intimacy.”

Roosevelt also institutionalized the position of speechwriter and understood the connection between words and policies and the importance of effective presidential communication. He collaborated with his writers, primarily Sam Rosenman and Robert Sherwood, describing his thoughts, sometimes musing, sometimes dictating. Kennedy had an equally close relationship with his lead writer, Ted Sorenson. Schlesinger quotes a Kennedy contemporary who said that “when Jack is wounded, Ted bleeds.”

Reagan allowed his writers to spend meaningful time with him so they understood not just what Reagan wanted to say but why.

It is taken as a given that the candidates who have been elected president excel at communications and by extension speechmaking. Schlesinger points out that is far from true and the lesson learned from his account is that giving a speech takes meaningful practice, both in drafting and speaking the words.

Some of the presidents who struggled the most with their speeches spent little time with their speechwriters or couldn’t completely grasp the why, or context. For instance, Lyndon Johnson would demand speechwriters include something that would generate a news story, regardless of the impact it might have on government agencies.

Richard Nixon would expect his team of writers to come up with anecdotes, when the most effective presidents were the ones giving the writers their own anecdotes.

More important, several presidents took office without ever having employed a full-time speechwriter. Harry Truman, Johnson, Gerald Ford, Jimmy Carter and Bill Clinton all had difficulties understanding the role of the speechwriting staff. Access was limited and so was the preparation.

Early in his administration, Clinton was notorious for making wholesale changes to his speeches moments before hitting the stage. Even George H.W. Bush, after spending two terms as vice president serving under a masterful communicator and employing the same speechwriter, Peggy Noonan, was uncomfortable bringing writers into his confidence.

In fact, he resisted staff recommendations to make a speech about the fall of East Germany, saying “I’m not going to dance on the Berlin Wall.” Roosevelt, Kennedy and Reagan would not have needed to be told to make this speech. Perhaps his son, the 43rd president, overcompensated for this missed opportunity when he made his infamous “Mission Accomplished” speech.

Obama has proven he knows how to combine words and presentation into a powerful address. If he’s elected, he will need to extend the rhetoric to action. John McCain would do well to spend some time reading this book. So far in this campaign, his words seem recited rather than being evocative. Using “White House Ghosts” as my guide, I’m guessing the candidate is not opening himself up to his writers.