We revisit anthropic arguments purporting to explain the measured value of the cosmological constant.
We argue that different ways of assigning probabilities to candidate universes lead to totally different
anthropic predictions. As an explicit example, we show that weighting different universes by the total
number of possible observations leads to an extremely small probability for observing a value of equal
to or greater than what we now measure. We conclude that anthropic reasoning within the framework of
probability as frequency is ill-defined and that in the absence of a fundamental motivation for selecting
one weighting scheme over another the anthropic principle cannot be used to explain the value of , nor,
likely, any other physical parameters.