The title of Errol Morris’ latest documentary, “The Unknown Known,” is an example of the verbal gymnastics employed by former U.S. Secretary of Defense Donald Rumsfeld when discussing strategies for any course of action.

What Rumsfeld means is that sometimes what we think we know, we don’t really know at all. That’s a pretty good description of how Rumsfeld himself, the subject of “The Unknown Known,” comes across in this film.

Rumsfeld certainly seems accessible (he reportedly spent 33 hours being interviewed by Morris) and willing to discuss any subject regarding his 40-plus years of government service — including his controversial stint as President George W. Bush’s defense secretary, helping drive America’s invasion of Iraq.

But he proves masterful at saying little about the consequences of his official actions. When asked, given that he was a hawkish architect of the war, if it was a mistake to have entered into it, he shrugs off the question by saying “time will tell.”

Unlimited Digital Access. $1 for 4 weeks.

Morris won an Academy Award for his 2003 “The Fog of War: Eleven Lessons from the Life of Robert S. McNamara,” a similar documentary about a more forthright former secretary of defense. This time he presents a portrait of a wartime leader determined to avoid, at any cost, an honest perspective.

Tom Keogh: