Language

What does 'all things equal' actually mean? I don't understand the expression at all. It surely isn't to be taken literally...unless one is constructing a thought experiment. But philosophers don't only use the phrase when constructing thought experiments. I'm lost.

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The Latin for the term is: ceteris paribus. When a philosopher is articulating a thought experiment, she may use the expression 'all things being equal' or 'other things being equal' / ceteris paribus, to put aside extraneous factors not essential to the thought experiment.

So, to take a simple example, imagine a philosopher is developing an argument from analogy for the conclusion that it is permissible for a nation to launch a preemptive attack against a nation that is threatening it. She might ask you to imagine the following: you are an innocent person and you are alarmed by the sight of someone you believe has assaulted and killed another innocent person drawing a gun and he appears to be getting ready to shoot you. Under these circumstances, when there are no police around and there is not time to run away or attempt to verbally confront the apparent assailant, wouldn't it be permissible for you to harm or perhaps even kill the person on grounds of self-defense? Why should you be compelled to allow the person to fire first? The argument may then go on: if it is permissible for an individual to do that, wouldn't it be permissible for a nation to launch an attack on another nation when it is reasonable to believe the nation is about to launch an immanent attack? Now, I am not claiming this argument is sound or brilliant, but when the person presenting the argument adds 'all things equal', she is asking you not to bring in other distracting factors such as the following: But image the person who seems about to attack you is your brother who saved your life as well as the lives of hundreds, the brother furthermore may be hypnotized or under the power of an evil scientist and so he is not responsible for his action, moreover the brother knows a secret formula that will rid the world of child poverty and if you don't kill him, he may be safely apprehended and the secret used by aid workers to save the lives of millions.

Actually, perhaps a better phrase than 'all things being equal' would be 'all things being normal.' In other words, once you have changed the thought experiment to involve a life-saving, hypnotized, brilliant problem-solving scientific brother, you have distracted our attention from the more central issue at stake: can the right to self-defense be extended to justify exercising preemptive, perhaps even lethal force?

Like any real experiment, a thoughtexperiment (or analogy, case study or example) in order to be validevidence for some position, has to be conceived of as beingrepeatable. So, my thought experiment should be compelling onits own terms, and not because of some special context that makes itcompelling. Only then will the thought experiment (or whatever) havevalidity beyond that context. 'All things being equal' is thus akinto the notion of controlling variables.

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