As Einstein said, "it's all relative". Nothing is perfect or absolute, only a fool would go about life with such a predisposition. However, some things are more rational or rather are closer to what one expects or demands of reality and the world around them than others. Knowledge, science, and logic has always been about testing the limits of pragmatism, or rather living by it, and seeking and testing it alongside long-held beliefs and ideas. Some theories produce greater works than others, this is the scientific process and perhaps the essence of pragmatism and maybe even ingenuity or possibly life itself. Who knows. Hm.. some may even say, the only non-rational decision one can make is choosing to blindly abide by, that is to say never deviate or rather consider the possibility of deviating from, what was rational or otherwise has worked in the past.

Again, who knows? That one shot you take in the dark may strike a target that is not present in the light of what is known or understood. Is this not how all invention and innovation came to be?

I don't know where I heard this but it's said that there are two important facts that each and every one of has to realize viz. there are things we can't control (ramdomness) like other people's behavior and there are things we can control which is our behavior. Rationality is about how we can plot our course through all the randomness by calibrating our own behavior to produce desired results.

'Rational' is that word which I don't think can ever be satisfactorily defined. You can eliminate every -ism except rationalism because once that's gone we have nothing left to talk about and philosophy dissolves.

So definitively, there are rational decisions -- all of the ones we can talk about.

I think this is a really good question. I take it to mean decisions free from any emotional pull, desire, bias, etc. With that in mind, I would say that some very mundane decisions are rational, like deciding the answer to 2+2 is 4, but that’s about as far as I am willing to concede. Environment plays an enormous role on our behavior, especially regarding our basic needs. Is the decision to fulfill our basic needs rational? I personally don’t think it is, and virtually every decision is made in order to fulfill some desire or need, which is necessarily subjective.

I very much agree with the sentiment and the conclusion that if it goes away, we might as well say random words or stare at a wall or something.

The problem would be, what do we do with terms like "irrational" or "sensible", etc.? Sure, you can pick out edge cases and say that is irrational, but outside these cases, one of these words are easy to develop.

If everything is the result of a complex interplay of randomness, how can any decision be truly rational? Do we make rational decisions, or is everything just arbitrary? — Cidat

There must be if anything is to make sense whatsoever. In fact, I'd say that even asking such a question presupposes that there must be rational actions. After all, you'd expect (mostly) reasonable replies.

what do we do with terms like "irrational" or "sensible", etc.? Sure, you can pick out edge cases and say that is irrational, but outside these cases, one of these words are easy to develop. — Manuel

I understand this is an argument from gradualism but I do believe it can be applied to any definition. In which case don't see the problem with starting from basics. 'Rational' can be coherently communicated. 'Sensible' can be physically grounded. If there is any implication that we 'must' refer to proper references like dictionaries to define our terms then I doubt this is necessary for most discourses.

Absolutely. In fact, this is what we do: we start with basic terms which we don't fully understand, but can speak about them in a manner that makes sense. Also correct about dictionaries, though they only give us the most superficial idea of a word. My personal puzzle if that, if we do stop and think about what a rational act entails, it all gets complicated very quickly. But if we don't stop to think about it, we are apt to using the word with less mistakes, or so it seems to me.

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Everything is not a complex interplay of randomness. Entropy imposes order - energy, causality, and the consistent movement of energy from higher states to lower states, which is to say, from before to after the energy event.

If everything is the result of a complex interplay of randomness, how can any decision be truly rational? Do we make rational decisions, or is everything just arbitrary?

I think that it the ultimate goal of all life is to continue. This being the case, any decision made with that goal in mind has to be viewed as being rational.