Reductionism reduces everything to its parts. You know how the parts behave, then put them together, and thus you know how the whole thing behaves.
This could be for our knowledge in principle, for our knowledge in practice, and for how the universe does it (except the universe doesn’t, we just think it does).
Reductionism has been exceptionally successful in the last thousand years or so, first with the Arabs and then with the Europeans and their descendants.
Holism considers things as a whole. You know the principles that govern the behavior of the whole, thus how the parts work isn’t important.
This could be for our knowledge in principle, our knowledge in practice, and for how the universe does things (except it doesn’t, we just think it does).
Holism was very successful for the Chinese and East Asians in earlier millennia.
So holism consider a thing as a whole, reductionism considers a thing reduced to its parts.
EXAMPLES
physics – chemistry – biology – psychology – sociology – history/economics/polisci
– geology – astronomy – cosmology
Pragmatism
This will seem like an unimportant digression, but it’ll bring us back to important things.
There’s a third way: pragmatism. Pragmatism is what do I need to know to get the job done. Pragmatism is less remarkable than holism or reductionism, it’s basically how we do things without thinking about them too deeply.
EXAMPLES
In chemistry one focusses on the periodic table and doesn’t worry about the quantum mechanics of electrons. You know the atoms, you know the shapes of the electron clouds (aka atomic and molecular orbitals), you know general rules like atoms on the left and right (especially upper right) parts of the table form ionic bonds, and the closer they are the more covalent the bonds are. You focus on thermodynamics without worrying about statistical mechanics. This is all mid-level stuff, particular to chemistry, not more fundamental fields like physics or more elevated fields like how much of each element did the universe synthesize and why.
So we have our mid-level or discipline-specific knowledge. It’s pragmatic. But how did we get here? It wasn’t ‘cuz our forebears stayed programmatic! They got holistic and reductionistic, and now we benefit by having knowledge that used to be out of reach.
HISTORY OF OUR KNOWLEDGE OF CHEMISTRY – HOW DID REDUCTIONISTIC KNOWLEDGE BECOME MID-LEVEL KNOWLEDGE
So the Greeks are the first recorded people to wonder if matter had individual pieces, which they called atoms, a name we revived when we found those pieces. But the Greeks wondered about a lot of things and got plenty wrong! In this case, atoms were so far more detailed than they had the capability to explore. Even things like making vessels out of glass – that’s important ‘cuz glass is pretty inert, so you can do many more experiments than you can in metal or clay vessels, and you can shape your glass in more ways.
The Greeks also thought the elements were earth, air, fire and water, and the fundamental properties were hot, cold, wet and dry. This was reductionistic: let’s reduce all matter and all properties to these four of each. They could explain some things: rain falls to the ground because both water and air have the property of wet, so they attract. It left a lot to be desired by our standards, but it was a decent start. Interestingly, reducing things to just four materials and four properties has holistic aspects: these few things govern and explain everything. Like yin-yang.
There was a lull for a millennium or so. Then the alchemists had more technology at their disposal (glass), and they had some holistic ideas to use and prove. Base metals to noble metals to life. The philosopher’s stone. Things like that. These were big principles that governed everything. They wanted to both prove them and use them. So they go to work and did lots of experiments. They weren’t thinking reductionistically exactly, but with experiments, records, and motives to achieve outcomes, they couldn’t help but being reductionistic. This led to the periodic table and chemistry. Also cells and biology.
So holistic ideas and reductionistic practice led to pragmatic, mid-level knowledge that was previously not knowledge at all!
READ FURTHER
The universe doesn’t think like we do
Very Universe 