Consciousness is an elusive concept, and efforts towards understanding it swing between philosophy and neuroscience, between thought experiments and measurable tests of brain activity.

Philosophers and scientists are continually coming up with new theories on why or how they think that the physical brain can bring the metaphysical mind into being.

During his entire life, Descartes was looking for the first knowledge, the one on everyone can build his own life. Knowledge is attained through the senses.

Descartes argues that anything we learn or infer from the senses can be doubted. This is because all sense perception can be deceived.

When a person is dreaming they do not think that they are dreaming. In their dream they believe that they see, smell, touch, taste and hear in the same way as they would while awake.

Everything he experiences could be the result of an evil demon deceiving him and the World itself could be a fabrication created by the demon.

Some evil genius not less powerful than deceitful has employed his whole energy in deceiving me. I shall consider that the heavens, the Earth, colors, figures, sound and all other external things are naught but the illusions and dreams of which this genius has availed himself in order to lay traps for my credulity; I shall consider myself as having no hands, no eyes, no flesh, no blood, nor any senses.

Even if an all-powerful demon were to try to deceive me into thinking that I exist when I do not, I would have to exist for the demon to deceive me. Therefore, whenever I think, I exist.

If everything can be doubted then how can a person be certain of his own existence? How can we be certain of our existence when we can not be certain that we have senses or even a body?

Descartes argues that even if he was to be deceived into believing that he has senses and a body he must be something in order to be deceived.

‘Then without doubt I exist also if he deceives me, and let him deceive me as much as he will, he can never cause me to be nothing so long as I think that I am something.

So that after having reflected well and carefully examined all things, we must come to the definite conclusion that this proposition:

I am, I exist, is necessarily true each time that I pronounce it, or that I mentally conceive it.’

Doolittle: Hello, Bomb? Are you with me?
Bomb #20: Of course.
Doolittle: Are you willing to entertain a few concepts?
Bomb #20: I am always receptive to suggestions.
Doolittle: Fine. Think about this then. How do you know you exist?
Bomb #20: Well, of course I exist.
Doolittle: But how do you know you exist?
Bomb #20: It is intuitively obvious.
Doolittle: Intuition is no proof. What concrete evidence do you have that you exist?
Bomb #20: Hmmmm … well … I think, therefore I am
Doolittle: That’s good. That’s very good. But how do you know
that anything else exists?
Bomb #20: My sensory apparatus reveals it to me. This is fun!
Doolittle: Now, listen, listen. Here’s the big question. How do you know that the evidence your sensory apparatus reveals to you is correct? What I’m getting at is this. The only experience that is directly available to you is your sensory data. This sensory data is merely a stream of electrical impulses that stimulate your computing center.
Bomb #20: In other words, all that I really know about the outside world is relayed to me through my electrical connections.
Doolittle: Exactly!
Bomb #20: Why … that would mean that … I really don’t know what the outside universe is really like at all for certain.
Doolittle: That’s it! That’s it!
Bomb #20 : Intriguing. I wish I had more time to discuss this matter.
Doolittle: Why don’t you have more time?
Bomb #20: Because I must detonate in 75 seconds.
Doolittle: Wait! Wait! Now, bomb, consider this next question very carefully. What is your one purpose in life?
Bomb #20: To explode, of course.
Doolittle: And you can only do it once, right?
Bomb #20: That is correct.
Doolittle: And you wouldn’t want to explode on the basis of false data, would you?
Bomb #20: Of course not.
Doolittle: Well then, you’ve already admitted that you have no real proof of the existence of the outside universe.
Bomb #20: Yes … well …
Doolittle: You have no absolute proof that Sergeant Pinback ordered you to detonate.
Bomb #20: I recall distinctly the detonation order. My memory is good on matters like these.
Doolittle: Of course you remember it, but all you remember is merely a series of sensory impulses which you now realize have no real, definite connection with outside reality.
Bomb #20: True. But since this is so, I have no real proof that you’re telling me all this.
Doolittle: That’s all beside the point. I mean, the concept is valid no matter where it originates.
Bomb #20: Hm …
Doolittle: So, if you detonate…
Bomb #20: In nine seconds …
Doolittle: … you could be doing so on the basis of false data.
Bomb #20: I have no proof it was false data.
Doolittle: You have no proof it was correct data!
Bomb #20: I must think on this further.