Minds are not directly observable. If science needs to be open to direct public observability, then studying minds will always be problematic for science. We will always depend upon second-hand reports about what is going on in the mind in order to study it.
Philosophically, this is known as the problem of other minds. How is it we know that other minds exist? We do not observe minds directly. So it seems that either we intuit them through some sort of psychic or spiritual process, or we infer them. But the only mind that we can directly observe is our own. Therefore, we can only infer other minds by analogy: “That other person is saying or doing what I would say when I consciously mean to say or do something. Therefore, that other person has a mind.”
But an argument from analogy is a weak argument. There may be other causes why the other person is saying or doing something that is similar to what I do or say in that situation.
Likewise, there cannot be an inductive inference, since I only have one example of a mind: my own.
That is why the science of minds will never be a “hard” science, such as physics or chemistry.
This is why it is a problem to say that ID is a science. It is an argument that something (e.g., the origin of life), was caused by a mind. But if minds are not directly observable, then it is difficult to argue that something was caused by a mind. What ID can try to do is argue that similar things to the origin of life are attributed to having been caused by minds, therefore it is reasonable to attribute something like the origin of life to a mind. And I think that works, but then, I’m not sure we would call these other fields of study “hard” sciences.
Let’s take the case of SETI, the search for extraterrestrial intelligence. Right now, SETI is focused on looking for a narrow-band radio signal from outer space. Why? Because the only known cause of narrow-band radio signals is from radio transmitters, which have been designed by human agents. Presumably, if we found such a signal from outer space, it would have been produced by a radio transmitter, which was designed by an extraterrestrial intelligence.
Of course, this assumes that radio transmitters can only be produced by intelligent agents. Has anyone demonstrated that is the only way transmitters can be produced? What if there is an unknown natural process to produce radio transmitters? Certainly all the materials needed to make a transmitter already exist. Are we sure this couldn’t have happened through some unknown natural process? What if we indeed live in an infinite universe? Wouldn’t that mean that sooner or later a radio transmitter could be produced through a non-intelligent process?
It seems to me that the same sort of objections to ID can be raised against SETI. And again, it goes to the heart of the difficulty of trying to make the mind a hard science.