Slippery slope takes the form of a valid deductive argument - i.e., a string of "if-then" statements which lead to a conclusion:
A -- > BB --> C
C --...--> H
But "H" in a slippery slope argument is roughly "Hell" - i.e., some condition or result which no sane, civilized, normal, right-thinking human being could possibly endorse. Implicitly, then:
~ H
And so, in an extended version of (deductively valid) modus tollens, the argument implicitly or explicitly concludes with the rejection of the opening premise:
A -- > BB --> C
C --...--> H
~ H
/.. ~ A
But: while deductively valid - in its informal and thus fallacious form, slippery slope involves "if-then" relationships (especially causal connections) which are not (as in the case of deductive logic) 100% absolutely certain.
(Remember: in a deductive "if-then" statement, the antecedent is not only a necessary but also a sufficient condition for the truth of the consequent: IF A is true, then B must be true.)
Rather, in the more inductive world refered to in slippery slope arguments, we simply cannot know ahead of time - with 100%, deductive certainty - that one or more of the If-then statements is true. (As well, slippery slope is often a close relative to "appeal to fear," insofar as it's "H"/Hell outcome is usually something used as fearful, threatening, etc.)
A classic slippery slope:
If we don't stop the Communists in South Vietnam, they'll take over the whole country.If they take over Vietnam, next they'll conquer Laos, Cambodia, and Thailand.
Once they have Laos, Cambodia, and Thailand - they'll overrun Indonesia and the rest of the Pacific Rim.
Once they conquer the Pacific Rim, they'll take Japan - and the next thing you know, they'll be off the coast of California!
[implicit: Communists invading California is unacceptable]
[explicit] We must stop the Communists in South Vietnam.
(The path of history and geopolitics is not easily captured in deductive syllogisms.)
1. Once a conservative like Ronald Reagan is voted in, then the fundamentalist
right, exemplified by the likes of Jerry Falwell, will gain in prestige and
influence in the political life of this nation. This will open the door to
Falwell and his cohorts establishing, say, ideological criteria by which
judicial candidates will be judged before submitting their nomination to
Congress. Once Reagan and Falwell have stacked the American judicial system
with judges who share their ultra-conservative ideology, it will then be
a short step to a theocracy in which the political leaders are at once the
high priests. So, for example, someone like Pat Robertson, host of the "700
Club" (a conservative religious program broadcast by satellite) will run
for President. The next thing you know, the goons will come around to collect
logic texts and philosophy professors for burning.
[Note: this example was written _before_ Pat Robertson ran for President
in 1988.]
2. If you don't get to bed early, you'll be too tired to do well on the GRE
tomorrow - and then you won't get accepted into a decent graduate school
and then you'll end up a washed-out alcoholic living in a trash-bin.
3. Scientists announced today (Feb. 24, 1997) that they had successfully cloned a mammal for the first time.
The technology thus exists (or will soon exist) which will allow us to clone genetically-identical copies of human beings as well. Given human beings' rage for personal survival, it will only be a matter of time before people will be willing to pay exorbitant sums for their own clone. And we'll be able to create entire "races" of clones, made specifically for certain tasks, thus returning slavery to human civilization - now made "clean" and efficient through biotechnology. In fact, I'll bet there's already a government project out there planning on using clones to create a superior race which will then enslave us all - just like "X-files."
We've got to stop this runaway biotechnology before we lose our freedom and our humanity!