[AskPhilosophers] Can premises be probabilities?

[Javier]

I was recently having a discussion with someone about the argument
from ignorance fallacy, or "absence of evidence is not evidence of
absence." We think that the following is a fallacy:

1. Alien spaceships orbiting the earth are observable through a
telescope.
2. No one has observed alien spaceships orbiting the earth.
3. Therefore, there are no alien spaceships orbiting the earth.

However, what if you changed the premises slightly to this:

1. Alien spaceships orbiting the earth would PROBABLY be observable
through a telescope.
2. No one has observed alien spaceships orbiting the earth.
3. Therefore, there are PROBABLY no alien spaceships orbiting the
earth.

Even though I agree with the conclusion, I think this argument is also
a fallacy since it follows the same form as the first one. But then I
seemed to remember from my deductive logic days that the premises of
an argument must be absolutes. You can't introduce probabilities,
otherwise the laws of logic do not even apply and all bets are off. On
the other hand, if the form of the argument is messed up, then does it
really matter whether or not the content of the propositions are true
or false? So do premises have to be absolutes in logical analysis, or
not?

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[Wicked2Sing]

Dear Javier,

Oddly enough, I am trying to tease apart this issue (being a new
student to this area of study) and have some thoughts on the
introduction of probability to your premises.

Formally, in the deductive method, you would have two "true" premises,
and together, they should combine to make an logical conclusion . . .
but could combine to make an illogical one. In the latter case, the
premises have not proven themselves to be "valid" and/or "absolute."
The argument should move from the "general" to the more "specific"
conclusion but fails.

In the inductive method, you could (more likely) have two premises
that would result in a conclusion with more of a "probability" of
truth, correctness, validity; within a certain percentage that the
"scientific community" would consider conclusive. The argument
demonstrating a movement rfom the specific to the general.

By introducing the word "probably," into your statement, have you
shifted your argument from deductive to inductive? Have you
introduced the element of "intention" to your statement, thus
accepting an acceptable spectrum of error?

Lost in space . . .

W2S