In this post I’m not going to do any exegesis on the text of the Aquinas’ fifth way, as defined in the Summa, but rather I want to think about the argument in light of recent expositions by the likes of Edward Feser and also think about some recent findings of science.
The argument, as far as my reading goes, is that each entity in the universe has a final cause - each entity is intrinsically orientated to some end or effect, and this can only be explained by a divine intelligence. The best analogy is with man-made objects - a hammer is directed towards driving nails. In a similar way, we can consider other natural objects as intrinsically orientated to certain ends. So, for instance, a heart is orientated to pump blood and you just could not give a complete description of a heart without talking about what it does, what it is “directed” towards doing. We can extend this to even the most basic building blocks of material reality. For instance, an electron is orientated towards a certain interaction with protons - in all and every instance, the interaction of a electron with a proton will result in an attraction between the two. Therefore, there is something intrinsic to the electron that contains information to “tell” it what to do when it comes across a proton.
I put “tell” in quotation marks, but it is very difficult to describe this final causality in non-anthropomorphic terms - I can’t think of how one would do it. One could argue that the final causality of an electron is based on the operation of some more basic building block, such as strings (however I would argue, that is the wrong way of looking at reality, but that is another story). However, this just pushes the problem along. Eventually we have to arrive at entities that are truly fundamental - these entities would be pure form, not being constituted by anything further fundamental. This form must “tell” the entity how to behave - it must not only contain information about itself (i.e. that it is the entity it is), but also about the other entities it is supposed to interact with. For those familiar with programming, it almost needs to be something like a class, with information about itself, and various methods containing if-then conditionals to instruct it how to behave.
What could be the source of such information? What holds these “instructions” constant? We have an analogy of such concepts in computer programming, but this of course is an activity performed by intelligent, sentient beings. Whatever the basic entity is, it surely isn’t an intelligent, sentient being - so it could not have somehow generated its own instructions or form within itself. The only other option, it seems to me, apart from these instructions issuing from a Mind, is that there just is no explanation for these forms - they just are, they just are the way they are and they just always stay the way they are, for no reason or cause whatsoever.
In light of these considerations, I think the only rational conclusion is that there exists some sort of designing Mind.