In my view, and I am the first to admit that this is not the only way to look at what philosophy is, is that philosophy is pre-science.
Philosophy is theory; drawing up theories based on evidence, but with less proof than what science needs to verify an event as science-discovered.
The theory of relativity is a perfect example. Einstein started with an assumption that the speed of light is the maximum attainable speed in the world. He then manipulated theoretical knowledge to describe the nature of matter as it approaches the speed of light. He was purely theorizing, and his theory involved math. He pointed at what could show that his theory is true, but he did not find this evidence. Other people found physical evidence that could neatly be explained by the Relativity theory. That's when his theory became science, scientific knowledge.
Another example would be the allegory of images on cave walls by Plato/Socrates in the Republic. The images and the conclusions drawn from the phenomena lead Socrates create the ideas of Forms and Ideals, things that are perfect, never change, last forever, and EXIST. This has not been shown to be a scientific fact, but Socrates pointed at the proof: we simply must discover the existing Forms.
The Relativity theory is science, but it started as philosophy. The theory of Ideals and Forms are philosophy, waiting to become science.
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Philosophy deals mainly or only in subjects that can not be scientifically decided. One branch is tautologies: math, logic. The other branch applies to phenomena in our physical world, and it is what pre-science is. Theories that may be true, but no additional evidence exists to make them true aside from the original assumptions or premises the theory is based on. For instance, the existence of a creator, omniscient god. The theory is infallible; God created the world, and he knows all that happens there. That's the entire theory of a creator god. It is true, inasmuch it can't be proven wrong. But no additional evidence exists that was discovered after the theory had been created, such as "you will see Jesus return and judge all souls, living and dead." God belief is a very neat and compact theory, it is believable, but it is faith-based because it can't be shown yet that it is scientific.
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Other unsolvable questions exist in philosophy: the classic ones deal with beauty, morals, and other elusive things, that can't be decided by logic or by evidence one way or another. What is beautiful to one person may be not to another; and neither is wrong or right, yet both will agree that beauty exist. So then what is beauty? The debate rages on.
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One unsolvable question was "what is ethics, what makes an action moral or immoral or amoral." This question has been solved, in a philosophical manner, which unifies the ethics field and creates a useful tool to explain it; however, it is still not science, hard evidence has not been found to show it is true, outside the realm of thoughts, observations and experiments that have helped create the ethics-solving theory.
This theory may or may not be true, but I haven't read yet a refuting theory against which it can't be defended using arguments. In other words, no valid criticism exists in response to it.
The text of the theory can be found in two links on this website. One link is a long-hand explanation, with some repetition and some explanations that are too detailed to the trained philosophers' eyes; the other link points at a skeletonized description of ethics, in a very short but idea-dense text.
The long text can be found here:
https://thephilosophyforum.com/discussion/10744/ethics-explained-to-smooth-out-all-wrinkles-in-current-debates-neo-darwinist-approach
The short, idea-rich text which is void of detailed explanation and of examples, can be found here:
https://thephilosophyforum.com/discussion/10903/shortened-version-of-theory-of-morality-some-objected-to-the-conversational-style-of-my-paper