[hamdani yusuf (OP)]

If you add enough "necessary axioms", you can end up believing whatever made them necessary. Hence religion, a flat earth supported on turtles, and other kinds of foolishness.

Better to start with observations.

The only thing we can be sure of is our own existence.  Any other things can be deceiving, including our observations.
An assumption is necessary if it can somehow be related to our existence.

[alancalverd]

Cogito ergo sum - or even sum - is actually an axiom since it can't be proved or derived from observation.

[hamdani yusuf (OP)]

Cogito ergo sum - or even sum - is actually an axiom since it can't be proved or derived from observation.

You can't be aware of your own existence while not existing. That's why this assumption is necessary.

[hamdani yusuf (OP)]

An assumption is necessary if it can somehow be related to our existence.

I'll try to elaborate this. Some of us might think that many assumptions in math don't seem to be related to our existence, and think that it would counter my assertion above.
But in many situations like war, the accuracy of our calculation based on correct mathematical assumptions can determine between winning and losing, between life and death. Hence they are necessary assumptions.

[marklivin]

If you add enough "necessary axioms", you can end up believing whatever made them necessary. Hence religion, a flat earth supported on turtles, and other kinds of foolishness.

Better to start with observations.

The only thing we can be sure of is our own existence.  Any other things can be deceiving, including our observations.
An assumption is necessary if it can somehow be related to our existence.

How can you be absolutely sure that we exist?

[alancalverd]

An assumption is only necessary if your argument or calculation can't proceed without it and you have no actual data. It's very important to label assumptions and question them if your observations don't match up to your expectations.

In war the only safe assumption is that the enemy is as clever as you are, and knows all your secrets.

Cogito ergo sum is essentially circular or axiomatic, but is not necessary if you base your arguments on observations.   

[hamdani yusuf (OP)]

How can you be absolutely sure that we exist?

Cogito ergo sum.
Is it possible for anything to be conscious while not exist?

[hamdani yusuf (OP)]

An assumption is only necessary if your argument or calculation can't proceed without it and you have no actual data.

You assume that your data is actual.

[hamdani yusuf (OP)]

Cogito ergo sum is essentially circular or axiomatic, but is not necessary if you base your arguments on observations.   

You interpret your observations using assumptions. You assume you're not hallucinating. You assume your instrumentations haven't changed significantly since last calibration, etc.

[alancalverd]

Doesn't matter, as long as the results are consistent. The sun always rises in the east, so I can deduce a consistent cosmology with no untestable assumptions. The day it doesn't, I'll review my cosmology, because in science the model is less important than the observation.

[hamdani yusuf (OP)]

Doesn't matter, as long as the results are consistent. The sun always rises in the east, so I can deduce a consistent cosmology with no untestable assumptions. The day it doesn't, I'll review my cosmology, because in science the model is less important than the observation.

Testable or not, true or false, you must make assumptions. You assume that the future universe will work the same way as it was in the past, and your current understanding about it is correct.

[alancalverd]

No, I predict that it will work the same tomorrow as today, and if it doesn't, I know my current understanding is incorrect. That's how science works.

[marklivin]

How can you be absolutely sure that we exist?

Cogito ergo sum.
Is it possible for anything to be conscious while not exist?

What if we are in a simulation and we have only the illusion of existence and thinking?

[Halc]

How can you be absolutely sure that we exist?

Cogito ergo sum.

The cogito part begs the existence, a fallacy. The ergo sum part is a non-sequitur, also fallicious.

Is it possible for anything to be conscious while not exist?

Which is sort of like asking if 3+5 is actually equal to 8, or only if 3 and 5 exist.

The point is mostly off topic. A universal moral standard need not 'exist' if it is a standard for a universe whose existence isn't distinct from its nonexistence. I deny such a standard, but that stance isn't a function of my stance on the existence of things. And besides, I probably have a different definition of 'being' than does Descartes. I go more along with Rovelli's definition, which is relational. Rovelli showed that one cannot collapse ones own wave function, therefore 'ergo sum' falls apart.

[hamdani yusuf (OP)]

No, I predict that it will work the same tomorrow as today, and if it doesn't, I know my current understanding is incorrect. That's how science works.

You assume that your current model of reality is the most correct one. There might be some observations that it can't explain, but no other model can do it better. So you stick to the current one.

In sociology of scientific knowledge, Planck's principle is the view that scientific change does not occur because individual scientists change their mind, but rather that successive generations of scientists have different views.

This was formulated by Max Planck:[1]

A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die and a new generation grows up that is familiar with it. . . . An important scientific innovation rarely makes its way by gradually winning over and converting its opponents: it rarely happens that Saul becomes Paul. What does happen is that its opponents gradually die out, and that the growing generation is familiarized with the ideas from the beginning: another instance of the fact that the future lies with the youth.

— Max Planck, Scientific autobiography, 1950, p. 33, 97
Informally, this is often paraphrased as "Science progresses one funeral at a time".
Planck's quote has been used by Thomas Kuhn, Paul Feyerabend and others to argue that scientific revolutions are non-rational, rather than spreading through "mere force of truth and fact".[2][3][4][5] It has been described as Darwinian rather than Lamarckian conceptual evolution.[6]
https://en.m.wikipedia.org/wiki/Planck%27s_principle

[hamdani yusuf (OP)]

How can you be absolutely sure that we exist?

Cogito ergo sum.
Is it possible for anything to be conscious while not exist?

What if we are in a simulation and we have only the illusion of existence and thinking?

It means that we exist in the simulation. It requires the assumption that the simulation exists, and implies that someone has built and run it. Those are unnecessary assumptions to explain observations, which can be explained more simply. It means we should discard the idea, according to Occam's razor.

[hamdani yusuf (OP)]

The cogito part begs the existence, a fallacy. The ergo sum part is a non-sequitur, also fallicious.

Any reasoning must start somewhere, which is the basic assumption. Otherwise, it would lead to infinite regress. It would prevent us from making rational decisions in a finite amount of time.

Why use reason?

We end up with capacity-circularity, which can't be a flaw in an argument, because it's not a property of arguments in themselves.
The capacity to reason isn't a premise or a rule, so the argument for its legitimacy need not be premise-circular or rule-circular.

This argument is closely related to anthropic principle and cogito ergo sum, which I've mentioned before.

[marklivin]

How can you be absolutely sure that we exist?

Cogito ergo sum.
Is it possible for anything to be conscious while not exist?

What if we are in a simulation and we have only the illusion of existence and thinking?

It means that we exist in the simulation. It requires the assumption that the simulation exists, and someone has built and run it. Those are unnecessary assumptions to explain observations, which can be explained more simply. It means we should discard the idea, according to Occam's razor.

I'd like to believe in it very much. But if we are really in the simulation, then the creators of the simulation exist (and even then not exactly), and we do not exist, because we are illusory.

[hamdani yusuf (OP)]

Which is sort of like asking if 3+5 is actually equal to 8, or only if 3 and 5 exist.

I think this is a false equivalence. Can those numbers have subjective experience?

[hamdani yusuf (OP)]

I'd like to believe in it very much. But if we are really in the simulation, then the creators of the simulation exist (and even then not exactly), and we do not exist, because we are illusory.

Even if we live in a simulation, it doesn't deny our existence. It just means that our forms and parts/components are not what we usually think they are.
Anyone who still exist now act as if they are living in a real world. Those who start to act otherwise won't last for long.