There are a few times in life when we take a leap, a leap of faith, a leap of trust.  There are the obvious big ones like taking a new job, or getting married.  And then there’s the smaller, less obvious one of giving a speaker an hour of our time.  We’re trusting that speaker to give us something new, something useful, and something authentic.

The key word is trust.  A study from the last century found that audiences want two things from speakers:  credibility and trust.   Credibility is obvious.  But trust?  I blogged earlier about the importance of making the audience think in a new way.

But let’s take trust apart a little more thoroughly, because it’s important.  There are two key components to trust:  credibility – do you sound like you know what you mean – and reliability – do you mean what you say?

Real trust takes time to develop.  Do you mean what you say in a variety of settings, from one meeting to another, from one year to another?  Do you follow through on the things you propose, offer, or guarantee?

But we have a kind of body language shorthand for trust that allows us to make a determination quickly in the moment as to whether or not we think a person is worthy of our trust.  And that is consistency between words and body language:  congruency.  We look for it, unconsciously, to see if we are comfortable trusting the person in front of us, provisionally.   When that person tells us something about her personal story, something affecting, does she seem to be reasonably emotional about it?  When that person talks about the opportunities lying ahead for the company she’s leading, does she seem reasonably excited about it?  And when our putative speaker tells us about wanting to combat malaria worldwide because of some village she spent time in, in sub-Saharan Africa, does her description of the suffering there correspond to a reasonably human reaction to that pain?

Congruency. It’s our first rough estimate of whether you, as a speaker, are trustworthy or not.  And it’s a tricky one.  For example, speakers typically walk on stage in a fight-or-flight state of mind – a state of nervous excitement.  And they start talking about their passion, their idea, or their cause.   But nervous excitement is not consistent with passion; passion is.  And so speakers undercut themselves from their very opening words.

We look to speakers for authority, and again nervousness doesn’t match our simple human estimation of what authority looks and sounds like.  Authority should be confident, right?  So why is the speaker sounding so shaky?

Speakers get into trouble this way, because of a mis-match between their intended message and our expectations of what their emotional states should be.  The mis-match doesn’t create trust and the speaker fails to win us over.  That happens, oh, once every 20 seconds somewhere in the world on a stage.

Here’s a simple trick you can use to increase your congruence as a speaker; or indeed, throughout your business career and its attendant meetings, conversations, negotiations and so on. Many people today speak as if every sentence were a question?  That is, they raise their voices slightly in pitch at the end of every phrase or sentence?

They do this probably because they’re seeking agreement, but the result is both incredibly annoying and lacks authority.  There is simply no way you can take charge of a meeting, your colleagues, or your career if you have this verbal tic.

I see it most with women in business, and with both men and women in businesses with a heavy emphasis on being collegial.  But however it happens, you must fight it.  Instead, begin your phrase or sentence at your normal pitch, allow it to rise during the sentence to show passion and energy, then bring it back down by the end to show authority.

This simple little trick alone has transformed the professional lives of some clients that we’ve worked with.  One in particular was offered a promotion to Vice-President, quit her job, and started her own company advising the organization she had worked for and others like it after we worked with her on the authoritative arc.

To see what I mean, study Martin Luther King, Jr’s “I have a dream” speech.  That speech, considered one of the best of the 20th century, perfectly exemplifies both the authority and the passion that the voice can project.  And it changed the world.  In it, King soars up on lines like, “I have a dream that my four little children will one day live in a nation where they will not be judged by the color of their skin but by the content of their character.”  At the end, he comes down back to his original starting pitch, and the result is powerful, persuasive, and authoritative.

Audiences want to trust you.  To create trust, you must establish congruence.  To do that, since you’ve been granted temporary authority as a speaker, you must speak with the authoritative arc.

Part of this blog post is adapted from my upcoming book on the science of influence, Power Cues: The Subtle Science of Leading Groups, Persuading Others, and Maximizing Your Personal Impact, due out May 13 from Harvard.  You can pre-order it here.