Does he love you? Check his grammar

"Wifey just got a new hair cut what do you guys think? I love it," Ashton Kutcher tweeted in 2009, along with a photo of a mohawked Demi Moore, circa G.I. Jane.

"I have the buzzer ready baby," she responded.

"I'm just playing baby but I think you'd look great with that cut."

"Thank you love. How 'bout I shave your initials into my head."

If you're analysing the couple's relationship by their tweets (and many people are these days) don't look at the subject matter. Look at the pronouns.

James W. Pennebaker, a psychology professor at the University of Austin at Texas, has developed a method for measuring the compatibility of a couple based on words like 'I', 'you', 'me', and about 180 others.

He calls them "function words" - those small, often ignored pronouns (she, he, I), prepositions, (with, but) and articles (a, the) - that he believes are something of a window to the soul.

"The way two people use function words with each other is a reflection of the patterns going on their mind," explains Pennebaker, who penned a book on the subject called, 'The Secret Life of Pronoun's. "It's a subconscious way of seeing if two people are on the same page."

While context, geographical and cultural backgrounds play a role in the way people carry on a conversation, what Pennebaker's really looking out for is whether two people are adapting each other's speech patterns. The more they mimic each other in the way they use words, the more sympatico they are.

In a series of studies, he found that when two people match function words in a conversation with each other - be it on email, Facebook, Twitter, or face to face - they are subconsciously connecting on a deeper level.

"It's a sign they're connecting, they're thinking alike," he says.

In one study of a group of speed daters, Pennebaker found that those who used function words in a similar manner were three times as likely to pick each other for a date. Comparing language in writing is just as revealing. In looking at the letters of married poets Sylva Plath and Ted Hughes, Pennebaker found their language patterns matched up less and less as their marriage dissolved.

But it's not just about love. Word match-ups are also a sign that two people fight well together. Based on Pennebaker's analysis of Rosie O'Donnell and Elizabeth Hasselback's arguments on "The View" they match pound for pound on speech patterns, though not at all on beliefs.

"It's more telling about whether the two people paying attention one another, and how engaged they are with one another," explains Pennebaker. "If two people are really connected they're having the same conversation."

Want to use his theory on your own relationships? Take a look at a recent email exchange. Do you start sentences the same way? Do you both use a lot of prepositions in your explanations?

If interpreting your romantic email exchanges grammatically feels a little too hyper-analytical (re: not cool) let Pennebaker do it for you. On his website, secretlifeofpronouns.com , you can actually copy and paste an email, Twitter or IM exchange and have it automatically analysed for compatability.

For my own experiment, I entered the Twitter exchange at the top of this post into Pennebaker's grammar calculator. The results: Demi and Ashton are not very compatible. Their haircut banter scored a .59 on a scale of .100. That's "far below average," according to the site, which gives an average score of .84 for most online exchanges.

To be fair, my language sample was small (it works better if you enter at least a couple hundred words for each person) and the way people write on Twitter isn't exactly a good measure of how they write or speak anywhere else.

But let's take their low score at face value. Back in 2009, when this Twitter exchange transpired, their language wasn't overlapping, and by Pennabaker's logic, that means they weren't thinking alike, which really means they weren't paying attention to each other. Most relationship experts would recommend a little affection as an antidote, a reminder of those three littler words, 'I love you'.

But if you ask Pennabaker, all that really matters is the 'I' and 'You.'