Question 34700
Consider an example log (-10) = x
The exponential meaning of this is 
10^x=-10
But no power of 10 can produce a negative number.
Oh?
What if we make the base -10 ?
Then (-10)^1 = -10
so, -10 works for this case; but what about (-10)^(1/2).
That is imaginary.  
Negative bases just don't give the properties that log
functions need.
So the base must be positive and its powers can never be negative.
Cheers,
Stan H.