Science is primarily about qualities - and only when we know the qualities can we coherently quantify.
This is the reality of the situation, and may conclusively be shown by philosophical argument; but the fact is nonetheless almost universally ignored, and almost as frequently denied.
(Indeed, it is a recurrent delusion in science that qualities can be derived from quantities, and many people delusionally suppose they are doing theory-free science, based wholly on measurements and statistical analysis.)
The deep question in science is therefore how we discover true qualities - or, how do we discover the primary phenomena; because only after these are known can 'routine' science get underway. It is qualitative discovery that does the heavy-lifting in science, and it is the activity where creativity is absolutely necessary.
How can we observe primary phenomena? The key point is that we cannot know in advance where or how we will find primary phenomena, and we know we have found a primary phenomenon only in retrospect.
Specifically, the primary phenomenon is known when the situation becomes simple, clear and obvious. We recognise that what we have before us (or in mind) is a primary phenomenon because it is simple, clear and obvious.
This accounts for the strong element of surprise in scientific discovery! We do this, then that, and then the other - then suddenly we see, grasp and know what is happening, what we are dealing-with!
We have arrived at a situation of simplicity, clarity; and it is obvious.
But how do we look-for it? Where do we look for it?
Well, there are no rules - and indeed the necessary capacity is the capacity of recognition. But science does imply purposive seeking, so what is happening? This can't be answered with precision but only by such hints as putting our minds to the matter in hand, attending to things with honesty, and observing various 'arrangements' of things (for example making structured observations or doing experiments).
We expose-ourselves to various things in a purposive manner while being alert and attentive... and then at some point we may recognise that we have before us (or in mind) exactly that situation of simplicity and clarity when the meaning is obvious. We experience the state of knowing.
It can be seen just why we cannot, in principle, know in advance what observations, what experiments will yield primary knowledge of this type - we don't know what exactly we need to do, because if we did we would already be knowing what we seek.
Yet how can we find what we seek given this; and given that the search-space would seem to be infinite? We have an infinite number of choices of what we might do - how does anybody ever discover the needle of a primary phenomenon in the infinite haystack of distracting irrelevance?
(Of course, sometimes the need is not found - but sometimes it apparently is; and even sometimes seems impossibly against the odds.)
I do not have an answer; and the point is that neither does anybody else - which is why science cannot be made into a process. There is no scientific method: there just isn't. Science - I mean real, creative, qualitative science - cannot be planned.
(Thus 99% of what calls itself science is a fake... probably more. Mostly is it merely measuring, parasitic-upon science)
How may primary phenomena be validate: in other words, how do we now that a qualitative phenomenon really is primary?
Especially considering that primary phenomena cannot be tested by measurements - because qualities are primary, quantities are structured-by the qualities. Measurements are made of and by-using the qualities - so measurements cannot evaluate their validity.
The true test of a primary phenomenon is that anybody competent and honest can, in principle, observe them - once they have been pointed-out, everybody knows where to find them.
But how do we know if someone is competent and honest? (And when they are not!)
The answer is: by exactly the same primary knowing as leads to the identification of the primary phenomenon. That is, we may get to know a person such that we know - simply, clearly and with conviction - that they are honest and competent.
And only such persons can do science. Anyone not so-validated must simply be excluded as generators of mere noise and distortion.
Science is difficult enough without letting-in nose and distortion! And too much n&d will render real science impossible.
This is why real science is always and necessarily done in 'invisible colleges' of not many people who know and trust each others honesty and competence.
(Again this emphasises the fact that that 99%-plus of modern, professional self-styled 'science' is nothing of the kind!)