Equivocation
Equivocation ("to call by the same name") is an informal logical fallacy. It is the misleading use of a term with more than one meaning or sense (by glossing over which meaning is intended at a particular time). It generally occurs with polysemic words (words with multiple meanings).
Albeit in common parlance it is used in a variety of contexts, when discussed as a fallacy, equivocation only occurs when the arguer makes a word or phrase employed in two (or more) different senses in an argument appear to have the same meaning throughout.
It is therefore distinct from (semantic) ambiguity, which means that the context doesn't make the meaning of the word or phrase clear, and amphiboly (or syntactical ambiguity), which refers to ambiguous sentence structure due to punctuation or syntax.
A common case of equivocation is the fallacious use in a syllogism (a logical chain of reasoning) of a term several times, but giving the term a different meaning each time.
Examples
In the above example distinct meanings of the word "light" are implied in contexts of the first and second statements.
Conditional entropy
In information theory, the conditional entropy (or equivocation) quantifies the amount of information needed to describe the outcome of a random variable 
given that the value of another random variable 
is known. Here, information is measured in shannons, nats, or hartleys. The entropy of conditioned on is written as 
.
Definition
If 
is the entropy of the variable conditioned on the variable taking a certain value 
, then is the result of averaging over all possible values that may take.
Given discrete random variables with domain 
and with domain 
, the conditional entropy of given is defined as:
Note: It is understood that the expressions 0 log 0 and 0 log (c/0) for fixed c>0 should be treated as being equal to zero.
if and only if the value of is completely determined by the value of . Conversely, 
if and only if and are independent random variables.
Chain rule
Assume that the combined system determined by two random variables X and Y has joint entropy 
, that is, we need bits of information to describe its exact state.
Now if we first learn the value of , we have gained 
bits of information.
Once is known, we only need 
bits to describe the state of the whole system.
This quantity is exactly , which gives the chain rule of conditional entropy:
Equivocation (disambiguation)
Equivocation is a logical fallacy whereby an argument is made with a term which changes semantics in the course of the argument.
Equivocation may also refer to:
Podcasts:
