Can we know things for certain?

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Subject classification: this is a philosophy resource.

Practically every person thinks they know things. Some people are even 100 percent convinced of the things they think they know. And then you have people who acknowledge they know nothing. But can you actually know things for sure? Does real knowledge even exist?

All we know is that we know nothing

Pro

• Pro Everything we have ever come up with about how everything works, functions and happens is just a theory.
  • Objection But we can observe and experience the world, right? No one would deny that the trunk of a tree is brown. So stating that a tree trunk is brown is based on the truth.
    • Objection Our mind can also deceive us, as Descartes explained. There could be an evil demon capable of manipulating everything from our thought process to our perceptions of our surroundings, making it seem as though something exists even when it does not. We see the tree trunk as brown, but perhaps it is actually red. Or maybe the tree doesn't even exist and is merely a product of our consciousness?
      • Objection What can we trust if there is a demon influencing our thoughts so that we cannot perceive reality? Does truth pertain to what we perceive as truth, or to a truth that no one can perceive?
        • Objection That is a fundamental question. If out of 100 people, 100 are 100 percent convinced that the tree trunk is brown, you should consider that as the truth. It could be that all the people are wrong and that the tree trunk is actually red, and that that is the real truth. You could say that, in the case that such a reality-undermining principle exists, there is a truth based on human agreements and consensus (everyone sees the tree trunk as brown, so it's brown), but there is also a truth based on metaphysical reality (the tree trunk is actually red, but no one sees it that way).

Con

• Con Through the scientific method, we can gain knowledge about how things work, function and happen.
  • Objection Science as we know it is dominated by scientism, which is based on positivism. Positivism is the philosophical view that only the empirical sciences—science based on experience, observation and experimental outcomes—provide valid knowledge. So it is not at all self-evident that the outcome of the scientific method is the truth.
    • Objection Such data is only considered the most robust and key – logical conclusion-making, knowledge gap identification, uncertainty evaluation, rational argumentation, and so on are all more or less part of scientific progress or the scientific approach. Usually or in general, it is admitted that even for the best proven things, with examples like the brain in a vat thought experiment making this clear, things could eventually be completely different but the likelihood is low. For things with high likelihood such as facts like "Earth is round", "Earth is a planet", or "Biological evolution is a true theory" it depends on the definition of "certainty" – these facts may be certain but not absolutely certain since there is a small chance we e.g. all live in a simulation where these facts aren't as true or even not true at all.
      • Objection Only the extent or scope of the veracity of statements like "Earth is round" would be altered if such conditions were met: in a simulation Earth would still be round, that statement may then only hold true within the context of simulation where the nature of reality that includes Earth would be altered with such an understanding.
• Con Every person knows that 1 plus 1 is 2. No one will deny or contradict that. That means this is the truth.
  • Objection Numbers are also only a creation of human beings. Numbers are an abstract idea and do not represent reality. The universe is more complex than just numbers.
    • Objection Not everyone shares this view. Pythagoras, for example, believed that, fundamentally, reality is made from numbers.