Phrase/word that is a synonym to "Question Everything"

What are some phrase/word synonyms for the phrase 'Question Everything'. My friend came up with nullius in verba, which I really like, and I was wondering what others are out there?

Edit (from comments): Perhaps synonym was not a good word-my vocabulary is not the best. I am just looking for phrases that portray a similar idea. The context would be potential tattoo phrases.

Solution 1:

Someone who questions is a skeptic. Dictionary.com:

1. a person who questions the validity or authenticity of something purporting to be factual.
2. a person who maintains a doubting attitude, as toward values, plans, statements, or the character of others.

Solution 2:

If you want an expression, a doubting Thomas may fit:

• a person who refuses to believe anything until they are given proof.

Usage notes:

• In the Bible, Thomas would not believe that Jesus had come back from the dead until he saw him. He's a real doubting Thomas - he simply wouldn't believe I'd won the car until he saw it with his own eyes.

Source: http://idioms.thefreedictionary.com/a+doubting+Thomas

Solution 3:

"Trust no one" and "trust nobody" come up often enough.

"Don't believe everything you read" (variant: "everything you hear") is a common saying.

Those both focus on the negative side. Some more positive options are "stay curious" and "seek the truth." (That's veritas quaere if you prefer Latin, and who doesn't?)