"Probably" is the most friendly and entertaining word in the advert, but it was put there for legal reasons:

"There's been an exciting level of debate about the campaign. Lots of you have asked why the word "probably" is included in the ad slogan, and stated that you'd prefer the wording to read "There's no God". While I fully understand this view, there's a vital reason for the "probably"'s inclusion: as with the Carlsberg ads, it's likely to get us around the advertising regulations (specifically points 3.1, 3.2, 5.1, 8.1, 9.1 and 11.1 in the general rules of the CAP Code, which regulates non-broadcast adverts in the UK). In my view, neither version of the slogan br...

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"Probably" is the most friendly and entertaining word in the advert, but it was put there for legal reasons:

"There's been an exciting level of debate about the campaign. Lots of you have asked why the word "probably" is included in the ad slogan, and stated that you'd prefer the wording to read "There's no God". While I fully understand this view, there's a vital reason for the "probably"'s inclusion: as with the Carlsberg ads, it's likely to get us around the advertising regulations (specifically points 3.1, 3.2, 5.1, 8.1, 9.1 and 11.1 in the general rules of the CAP Code, which regulates non-broadcast adverts in the UK). In my view, neither version of the slogan breaches the code, but CAP has advised that "the inclusion of the word 'probably' makes it less likely to cause offence, and therefore be in breach of the Advertising Code."

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Should have read my own article more carefully:

There's another reason I'm keen on the "probably": it means the slogan
is more accurate, as even though there's no scientific evidence at all
for God's existence, it's also impossible to prove that God doesn't
exist (or that anything doesn't). As Richard Dawkins states in The God Delusion,
saying "there's no God" is taking a "faith" position. He writes:
"Atheists do not have faith; and reason alone could not propel one to
total conviction that anything definitely does not exist". His choice
of words in the book is "almost certainly"; but while this is closer to
what most atheists believe, "probably" is shorter and catchier, which
is help...

Should have read my own article more carefully:

There's another reason I'm keen on the "probably": it means the slogan
is more accurate, as even though there's no scientific evidence at all
for God's existence, it's also impossible to prove that God doesn't
exist (or that anything doesn't). As Richard Dawkins states in The God Delusion,
saying "there's no God" is taking a "faith" position. He writes:
"Atheists do not have faith; and reason alone could not propel one to
total conviction that anything definitely does not exist". His choice
of words in the book is "almost certainly"; but while this is closer to
what most atheists believe, "probably" is shorter and catchier, which
is helpful for advertising. I also think the word is more lighthearted,
and somehow makes the message more positive.

Ariane Sherine