In common usage, the antonym for "faith" is "doubt." Certainly that would be true in most churches. I think the reality is different. I think the word, "certainty" is a better antonym and that faith and doubt are more like fraternal twins... not exactly the same but very, very closely related.
Let me explain. Both faith and doubt require a bit of humility that says, "I'm not entirely sure." Faith, the book of Hebrews tells us, is "the substance of things not seen." That is to say, it is the things about which we cannot be 100% certain. We've looked at the evidence and at our experience and everything points that way. We've wrestled with the question and have come up with the best possible answer, but we don't have all of the data and there is no formula to get a scientific provable answer. Any answers we do have are written in pencil as they are subject to change. We have faith. We aren't sure. Likewise with doubt, we have wrestled with the questions and looked at all of the available data and it just doesn't seem to point at the commonly accepted answers. It doesn't feel like the answer that is presented to us is the best answer and maybe there isn't an answer at all... but we still aren't sure. We have doubt. There is room to revisit the questions.
Both leave room for more growth and more possibilities. Both imply that the questions are more important than the answers and the wrestling is more important than reaching conclusions. Indeed, as soon as a permanent conclusion is reached, we are no longer in the realms of faith and doubt, but of certainty. That is not a good thing. Certainty has no room for any other possibilities. There is no wrestling. There are no other possible answers. There is no room for discussion. There is no growth yet to come. All humility goes out the door.
If my analysis is at all correct, it has huge implications for those of us who call ourselves followers of Jesus. We are not called to certainty, we are called to faith. The journey of faith does not come to an end because there is no end. Instead we move back and forth between doubt and faith, struggling with the difficult questions of life. Sometimes we are strong in our faith. Other times we are full of doubt. Both are essential steps on the path. Certainty takes us off the path, impedes our progress and our growth, and keep us from knowing the wonders we have not yet seen or experienced.
So hold fast to your faith... and your doubt. Both are positive steps along the journey to which we're called.