Evolution is a phenomenon.
A phenomenon is an occurrence, a circumstance, or a fact that is perceptible by the senses (Source: http://dictionary.reference.com/browse/phenomenon, accessed Sept. 17, 2012).
What humans perceive is that populations of living organisms have changed and are changing over time.
“The theory of evolution” is shorthand for the set of explanations that seek to explain the phenomenon of evolution. Sometimes “the theory of evolution” is also called “evolution,” and this can be confusing.
Really, the theory is “the theory of evolution BY natural selection, genetic drift, gene flow and mutation.” In science, a theory is a set of well-tested hypotheses and repeatable experiments that together provide an explanation for a phenomenon.
Again, evolution is the phenomenon.
Scientists have demonstrated that the processes, or mechanisms, of natural selection, genetic drift, gene flow and mutation, together explain WHY and HOW the phenomenon of evolution occurs.
If you want to be clear, you should use “evolution” to refer to the perceivable fact and “the theory of evolution” to refer to the scientific explanation for why and how evolution occurs.
To be even clearer, you should say, “TTOEBNSGDGFAM” for “the theory of evolution by natural selection, genetic drift, gene flow and mutation.” Pronounce that any way you like, I suppose.
There are not currently any scientific alternatives to TTOEBNSGDGFAM.
So, any legislation that states that public school teachers should be able to teach alternatives to TTOEBNSGDGFAM in their science classrooms is bad legislation that is not based on valid science.
Public school science teachers who state in their classroom that evolution is not a real phenomenon and/or promote (or denigrate) non-scientific views regarding the origins and diversity of life on Earth are at risk of violating the Establishment Clause of the First Amendment of the Constitution (i.e., breaking the law).
p.s. The theory of gravity seeks to explain the phenomenon of gravitation.