What is “fundamental” in physics?

Question

Sorry about the broad question. I'm still learning to frame the questions on Physics OverFlow.

Currently researching the nature of interactions in philosophy.

My question is: When physicists use the term "fundamental", what do they mean?

In philosophy, most seem to claim that to be fundamental means to be the source of causal power. That is, to say that quarks are fundamental means that if we can find exactly how quarks interact, we can explain all phenomena in the world because everything is made up of quarks after all (the behavior of quarks is the primal cause for all phenomena). And philosophers also tend to handpick findings of physical sciences to support this claim.

I sense that this might be an incorrect picture and want to understand what fundamental means in physics to be able to clearly write why we might be using a mistaken notion of fundamental.

Thank you for your patience!

Comments

Fundamental means relevant for the foundations of a subject matter.

Since the perception of what are the proper foundations is somewhat subjective, the same holds for the term fundamental. 

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@ArnoldNeumaier Thank you for the reply.

1. Would it be correct to say that quarks are more fundamental than atoms?

2. Can we understand it as: within physics, quarks are fundamental while say, in biology, they are not? If yes, would we say it is because they study different kinds of objects? My focus is also on how we classify. This would help in researching that. 

Thank you so much for your guidance! 

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@sahanarajan18: What is considered as fundamental depends on the description level.

In elementary particle physics, quarks are fundamental. In nuclear physics protons, neutrons, and mesons are fundamental, in quantum chemistry, nuclei and electrons are fundamental, in molecular biology, amino acids and nucleotides are fundamental. 

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There can be two meanings, depending on how we view models in physics. The foundations of a particular class of models are just the parts and concepts from which those models are built up; indeed, insofar as they're mathematical models, the foundations may be definitions and axioms.
The second level depends on how we view the relationship between our models and the real world and on how we view failed theories. There was, for example, a fairly long period when phlogiston was a real thing to scientists, but that idea was eventually discarded in favor of better models; the hard and perhaps impossible question is whether the idea of quarks (or any other idea in physics) is a modern phlogiston or not. A hard-edged realist could say that something is a foundation only if it will never be discarded in favor of something else. I think choices about realism-vs-anti-realism has to be said to be very personal, insofar as one finds both philosophers and physicists taking both sides of this divide (and of course various in-between positions). One thing to research is the "pessimistic meta-induction" (google gives us the SEP page, https://plato.stanford.edu/entries/scientific-realism/).

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@PeterMorgan Thank you for clarifying! It is really helpful to have the SEP reference as well! Will look into them.