If the world is not rational, science is not possible.

The world is not rational, because rationality belongs to sentients, not to planets.

If the universe does not work in rational ways then no useful thinking is possible and we might as well just do whatever we feel like doing from moment to moment.

The "world" is neither rational nor irrational. People think in rational or irrational ways or combinations of both.

Even if everything outside the person studying something were irrational, the conclusions of a rational person can still be observed.

Why can we be certain the scientific method works to tell us "truths" about the universe?

What is the basis of the "truth" of the scientific method?

Is there a single word I could have used instead of rational to pass Rachel's linguistic test?

Whether the world "is" rational or not is irrelevant. All that matters is that we can build a rational model for it.

D'A

Also, you're fundamentally confused about the purpose of science. "Truth" doesn't enter into it.

D'A

D'A:

What is the purpose of science?

The purpose of science is to provide useful predictions about the future state of the world and the results of our actions. Science is useful to the extent that the world is predictable. If the world does not behave in predictable ways, then science is not useful. Fortunately, so far, many phenomena have been observed to be very predictable.

The more irrational the world seems, the more valuable science can be.

Just because you do not recognise the laws does not mean they no longer exist.

Ah, I suspect what we have here is a failure to understand complexity theory :-)

Here goes:

1: The world is made up of lots of random events.

These are absolutely random, in the sense that there is NO WAY to predict how a particular "event" will turn out. This is not a matter of us "not understanding enough" - it is (at least, to the best of our understanding) part of the fundamental nature of the universe.

2: While we don't know how the events will pan out, we do understand some of the probabilities.

Consider drawing cards from a random deck. You don't know which card you will draw... but if you draw a card 100 times, you'd expect that ABOUT 250 times, you'll get a heart. Actually, it almost certainly WON'T be 250 times... but it's pretty likely that it will be somewhere between 240 and 260 times.

3: You might have thought that a small difference in how something starts off would only make a small difference in how it finishes, but sometimes you'd be wrong in making this assumption.

For example, the difference in a gust of wind coming in the door in my local pub just as I'm throwing a dart wouldn't really make a difference in whether I hit double-top or not.

... however, our intuition about how MUCH small variations make a difference, and how complex the knock-on effects are tends to "over-simplify." In fact, the fact the door opened at just the wrong time made me hit single top rather than double, because I was already aiming low - as a result of that, Steve won the match, and I had to buy the drinks. This resulted in me not having enough cash in my pocket to get the bus home, so I walked. This was blinding good fortune, because that evening, the bus crashed, and everyone sitting upstairs was rushed to hospital... so the net result of the door opening a few seconds later would have been that I'd have spent the night in hospital rather than watching the late movie.

The purpose of Science is to apply a standard methodology to working out the probabilities, and trying to assess what the impact of the probabilities would be.

Science is LOUSY at modelling whether I watch the movie or go to hospital as a result of the door opening timing...

Science (probability) is GREAT at modelling whether, over the next 100 darts matches with Steve, I'll end up buying more drinks than Steve does... because in science, you look at the last 100 darts matches I had with Steve, and notice I won about 80 of them!

The point about science is that it removes the "depends who's asking" factor - anyone else who studied my darts form would come up with the same assesment - that me playing Steve every night ended up with my getting a lot of free drinks :-)

So, even in a world dominated by inherently random things... Science has TREMENDOUS value.