What is metaphysics? In order to clarify and explain, I will use an example.
Metaphysics consists of statements about the basic structure of reality- metaphysics is the statements, it is not the reality itself.
And because it is the statements, any statement may be misunderstood - furthermore any finite statement must usually be assumed to be an incomplete and therefore biased summary of the totality of reality.
(Can we really expect to capture the fundamental nature of reality in a few sentences?)
But strictly, to assert that reality is more complex than the set of statements about reality is already doing metaphysics.
Here is one of my metaphysical beliefs: Everything in the universe is alive and to some extent conscious - all differences in consciousness are difference of degree; however, these differences in aliveness and consciousness are very great.
This exhibits many of the characteristic features of metaphysics. It is obviously a statement about the fundamental nature of reality. And, as such, it is not something which can be proven or disproven by observation or investigation.
For example, a scientist could not report that he had disproven my thesis by finding something that was not alive. If he did claim this, then the response would be that everything is alive - therefore there was something wrong with his research: either his concept of 'life' is incomplete, or else his instruments are too insensitive, or he just made a mistake... but the real problem is that the metaphysical aliveness of everything is assumed - it is not a scientific hypothesis to be tested, it is not some kind of inferential conclusion derived from multiple observations.
So, if this metaphysical assumption is in place, then all possible science is an investigation of living things - more-or-less living things, with different types of consciousness.
The typical modern mind would tend to say, at this point, that if that is so - and science cannot prove or disprove metaphysics, then metaphysics is serving no function and does not make any difference. We could say that everything is alive, or nothing is alive - science cannot test either statement - so it makes no difference which statement we choose to believe.
However, in practice this is not true. It would be true is a single metaphysical statement such as 'everything is alive' was assumed perfectly to capture the whole of reality. But because each metaphysical statement is assumed to be an incomplete and biased statement of reality, then we can, should, in practice must evaluate metaphysics in terms of systems of metaphysical assumptions.
So, on its own, a metaphysical statement seems a pointless thing - but in real life, each statement is part of a jigsaw.
Think of the first metaphysicians - the Ancient Greeks. Some said everything stays the same and change is an illusion, some said everything changes and stasis is an illusion - Plato said some things are eternal and changeless while other things do change. When I read about this as a teenager it seems like silly quibbling over nothing.
But the meaning of these metaphysical differences was embedded in the lives of the philosophers, and their general world view. Those who said everything stayed the same were concerned that otherwise nothing would have any identity, or meaning - all identity and meaning - all possibility of knowing anything about anything - would be swept away. Those who said everything changed were concerned about different matters: they focused on the fact that in the world as we see it, there is movement, there is birth, growth, ageing, and death - and their metaphysics puts this 'common sense' reality at its heart.
So, what about 'everything is alive and conscious? What difference does that make compared with the alternatives? Well, the difference is one in the context of life in this world - and how we actually interpret and react to life versus not-alive. Somebody might argue that 'everything is alive' amounts to the same thing as 'nothing is alive' - but that would only be true if each single statement was regarded as capturing all of reality perfectly.
However, if we assume that each metaphysical statement exists in a context of other metaphysical assumptions, then 'everything alive' is recognized as very different from 'nothing alive'.
Alive carries implications of some kind of purpose, consciousness, self-causality, relationship with other living things; but not-alive carries very different and opposite implications such as passivity, being a consequence of causes, purposelessness. For instance, an alive thing can suffer, a not-alive thing cannot.
What about the alternatives to these metaphysical statements of everything versus nothing being alive? Well, other possibilities include that some things are alive - and that things are neither alive nor not alive.
Some things are alive requires that we be able to distinguish between those things that are alive, and those that are not. This used to be regarded as straightforward, but is now regarded as so problematic as to be impossible - in the past the grey area (such as viruses or prions) between alive and not alive was regarded as not-affecting the argument - nowadays the existence of a grey area is regarded as invalidating the distinction between alive and not alive -- for moderns 'grey area' = no-difference.
That is the context of modern metaphysics - one in which any imprecision, overlap, blurring, ambiguity, problem of classification, even a hypothetical or imaginable grey area in a 'thought experiment' - is taken to invalidate distinctions.
So much so, that modern biologists have all but given up talking about 'life' and have thereby destroyed the foundations of their own subject.
(Which does not trouble modern biologists so long as they keep getting jobs, promotions and grants - the vast majority of modern biologists are not scientists engaged in discovering the truth about reality; but bureaucrats attempting to survive and grow their bureaus in competition with other bureaucrats - and so modern 'biologists' are happy to 'think', say or do whatever-it-takes to sustain their careers.)
So, the actual situation concerning the question of 'what is alive' is one in which we are forced either to say everything is alive and conscious (in different degrees and ways) - which means treating everything as purposive and in-relation on a continuum of alive/consciousnes-ness -- Or assuming nothing is alive and treating everything (including humans!) as purposeless and fundamentally isolated entities - subject to causes but themselves unable to initiate action - which is pretty much what has happened, but implicitly.
Or else, simply not to discuss aliveness - to rule-out the subject matter, stop thinking about it - make the subject unfashionable, regard such discussions as gauche, naive, childish - which is also what has happened within the subject that used to be defined as the study of alive things.
So, metaphysics does make a difference, and does matter in practice - despite that metaphysical statements cannot be tested by observation or investigation. Metaphysics makes a difference because it 'sets the agenda' for observation and investigation; and because each metaphysical statement exists in a context, and therefore has consequences.