"Faith" can mean belief without (or contrary to) evidence or argument; it can also mean rationally justifiable trust or confidence. "Doubt" can mean skeptical, evidentiary inquiry, or it can mean an emotional state of indecision and angst. "Rational" can mean holding a belief on the basis of evidence or argument, or it can mean objective, unbiased, or unemotional; likewise "irrational" can mean holding a belief without sufficient evidence, or it can mean biased, or emotional, or it can just indicate a motivation one disapproves of. Some words, such as "cleave" or "temper", actually have contradictory meanings.
In informal conversation, the various meanings of these words can usually be disambiguated by context: only one variant "fits" the context sensibly. In any kind of formal sense, though, the equivocal meanings of natural language words creates confusion, usually confusion fatal to understanding reality.
Even the very best philosophers have been sucked into equivocation fallacies. The meanings of words overlap so much that you can prove anything by adjusting meanings little by little over the course of an argument until you've proven black is white, night is day, freedom is slavery, or Republicans are truly concerned with the well-being of the poor. It really is not just possible but easy to erase any distinction by employing the equivocations inherent in natural language, with the defense, "It's in the dictionary!" valid at every step.
(For this reason, I think the project of pure analytic philosophy — using the meanings of words as one's metaphysical foundation — is hopelessly doomed.)
Computer programmers such as myself are, I think, especially aware of equivocations. Everything has to be very precisely and univocally defined; if it's not, the program crashes. If some term in computer programming has more than one meaning, it's useless. "Integer" is meaningless: I have to know precisely which kind of integer — signed? unsigned? 8-bit? 16-bit? 32-bit? two's complement? big- or little-endian? — your function requires as a parameter. So every concept, however it trivially differs from another concept, requires either a new word or a modifier attached to both meanings. It's no surprise that in just a half-century, computer programmers has generated more esoteric jargon than the medical and legal professions have generated in millennia. We have to think precisely, the computer doesn't cut us one bit (pun intended) of slack.
The equivocation fallacy underlies many specious arguments about similarity. Skeptics and theists both have faith, so they're both more similar than they're different. Well, not really. The concepts that "faith" labels are substantively different. Yes, the dictionary definition of "faith" covers both concepts, and in informal speech the the correct concept is implied by the context. But in a philosophical or intellectual argument, that disambiguating context is completely lost. That the same word is used to refer to two different concepts creates the illusion of deep similarity where only a superficial similarity exists. Both skeptics and atheists actually believe what they believe, they are in some sense committed to their beliefs; hence both have "faith" at this superficial level. But "faith" denotes also a specific underlying basis of that commitment: commitment without our in spite of evidence and arguments, a basis not generally employed by skeptics.
Silly you say? How could anyone make such an elementary mistake? It's easy. Google "atheism takes more faith than theism" (without the quotation marks) and you'll get a half-million hits.
Equivocate the dictionary and informal meanings of "irrational" as (1) unsupported by evidence or (2) emotional or (3) deprecated or (4) regrettable, and you can prove that religious faith — or by extension any false and unsupportable beliefs about race, sex, sexual orientation, history, nation, culture or ideology — is just another expression of the ordinary human condition, which we erase at the peril of becoming automata.
I understand, for instance, that Greta Christina is making a plea for tolerance. We skeptics aren't perfect, she seems to argue, so we shouldn't be too hard on the religious. It's all the same sort of ineluctable human irrationality, isn't it?
Well, yes and no. On the one hand, I agree we should be tolerant to some degree on general principles. We're all imperfect human beings, and we do need to cut each other some slack.
On the other hand, skeptical "irrationality" is different from religious irrationality. Really, fundamentally, substantively different. Just as with "faith" there are some superficial similarities, but the differences are far deeper and more profound. To use the same word just begs for the reader to ignore this substantive difference.
On the gripping hand, people under the spell of truly irrational ideas — and yes, not all of them are theists — all too often tend to kill other people... in large numbers: by the train-load, by the millions and tens of millions. They torture, imprison, exploit and oppress others in an orgy of human suffering that makes any sensitive person weep and despair for the future of humanity. And they do so for what they sincerely and deeply believe are not just good but heroically good reasons.
People who exhibit only the skeptical faux "irrationalty" (mistake, errors of judgment) just don't do that. Ever. They argue, they say mean things, but they don't pick up guns and start blasting abortion doctors, they don't fill concentration camps or gulags, they don't starve out peasants by the millions. They don't have Inquisitions, Crusades or Jihads, pogroms, auto da fes or Cultural Revolutions.
Voltaire said, "Those who can make you believe absurdities can make you commit atrocities." The belief in absurdity is not sufficient to commit atrocity, but it is necessary. And skeptical thinking, a deep and sincere commitment to rationality, is the only protection against absurdity.
An equivocation fallacy that obscures and trivializes a difference — i.e. between rational people and irrational people — that is profoundly and deeply morally relevant is not just weak philosophy, it can have murderous consequences. You'll pardon me, I hope, if my liberal tolerance has some boundary.