Reason is another faculty of the mind. Reason is the taking in of information, thinking about it until it is understood, and then forming a judgment. The process of doing those things in logic, and logic requires that the process of making judgments is based on valid information - or truth.
Let's take a look always at mankind's frame of reference; the judgment call used when Adam and Eve ate of the forbidden fruit.
The judgment was: Shall I eat or shall I not eat? of the fruit of the tree of the knowledge of good and evil. Since a judgment call was made this first time in recorded history, it would seem that our subjects already had in place the faculty of reason. they surely did because they were made in the image of God who is a reasonable and just God.
Part of the judgment process is possible outcomes. There were two: (1) Thou shalt die or (2) Thou shalt not surely die. These two possible outcomes were provided by (1) God, and (2) the serpent; respectively. A decision had to be made, judgment was necessary, and the process was called reasoning.
In this case part of the information was wrong. Logic requires valid information, and the consideration of it. For instance, if we were eating ice cream we know for sure if we don't eat it soon, it will melt. So to eat it ASAP or later is a judgment call based on valid information. If we're told that it won't melt, we must either believe that or not. If the decision is to wait awhile before we eat it, the logic is based on a falsehood, and a poor decision results.
Looking at our subjects, God told them that they would die. Was that truth or a lie? Obviously, neither died. In fact Adam saw that Eve didn't die, so he followed suit and ate of the fruit. In effect, the question of validity was: Is God lying about dying or not? Both believed the serpent rather than God because they both ate of the fruit. Eve blamed the serpent and Adam blamed Eve!
In order to use logic, reasoning must use valid information. They effectually called their Creator a liar, and believed the wily serpent. No wonder God was angry with them! God is truth! If you fail to believe that, look it up. We must always believe the Word of God, or we are mere neo-Adamic. Many Christians deny that God is truth. As example, God lied about the creation. Evolutionary Christians (my coinage) believe the serpent and not God. The serpent represents the world and is whoever deceives.
God meant, that they would lose their immortality. Adam and Eve failed to understand! When they were created, the design intent was to live forever! What God meant when he said, "You shall surely die,: is that rather than never feeling the sting of death, sometimes in the future they would die. Because they didn't reason with that information, they soon would suffer death. They both thought that immediately after they ate of the fruit, that they would die. Immediacy is another trick in Satan's repertoire. Pleasure is often provided immediately and most people seek immediate gratification. On the other hand, contentment and happiness are hopes which come about with time. The former is temporal and the latter eternal. Even if they had known that death was to come in 900 years, Adam and Eve would still have eaten because like us, they wanted immediate gratification. Something that distant in time was speculative, but what they had now was certain!
God gave truthful information. However, Satan parsed that truth with a little spin of his own. He knew that Adam and Eve didn't have full comprehension. They failed to realize by not understanding the death fully - that it is time dependent. God created time for mankind, and Satan used time to fool his victims.
Let me deviate a little bit. We too must be careful with the time element. Time deceives us. Just as God meant you shalt die someday when he said "thou shalt surely die", the same holds true for life. When he said ye shalt be saved, we take that as immediately, but it's sometimes in the future. Of course it may be tomorrow, but it may be in eighty years. Arminians believe that the day of salvation is at the time of death, which makes sense, because we are saved from damnation which commences at the time of death. Just as Paul uses the term the hope of salvation, Adam and Eve had the hope of eternal life - immortality, until it was spoiled by disobedience. We must be careful of the serpent's toying with our understanding as well! Looking at salvation in immediate terms can lead to a sinful lifestyle because people are misled into believing that faith is of short duration. When God said by faith you are saved, he meant enduring faith because non-enduring faith is an oxymoron! The hope of salvation is made safe until the time of death.
Back to the faculty of reason now. God provided utmost truth. The serpent distorted truth. However, using logic, they came to the wrong conclusion - at least Adam did, when he saw that Eve didn't die. They both thought about what they were seeing and hearing. Thinking is part of reasoning. They both saw the tree - it was real, the fruit was appealing, and the tree was beautiful. The serpent told them it was good for food and would make them wise. They took this information at face value. Dispensationalists call this the age of innocence. Thus far, they had never heard a lie, and didn't have understanding. Satan used their lack of understanding to deceive them.
It may be that the tree was good for food and would make them wise, but we still don't know those things. Sure, the fruit tasted good because Eve recommended it. That doesn't mean it was good for food! Even delectable candy can be poisonous. Eat too much of it and see what I mean! We can see that the fruit certainly didn't make them wise because immediately they tried to cover their own sin, and mankind has been trying to do the same ever since! You see, the deception and "wisdom" was forever. Satan uses truth and deception together to deceive.
So far, Adam and Eve used reasoning. We see that there was much that they failed to understand. They accepted falsehoods as truth - that is illogical. Then each formed a judgment. Adam's, seeing that Eve didn't die when she ate, he ate! He believed the serpent over God. He made a bad judgment call. At least he used data, although it was misunderstood - Eve didn't die! On the other hand, Eve's logic was even less! She just believed the serpent without any evidence of any kind! No wonder Adam was to have dominion but even he didn't deserve his grant.
The western world went from the age of faith to the age of reason. The former is theism and the later deism - the first is Latin for belief in God, and the latter Greek for the same. You see, Deism is based on reason, and the serpent still uses partial truth to deceive. Thomas Paine accelerated Deism by his pamphlet The Age of Reason. He deceived the western world and even many of our founders!
Thomas Paine also poisoned the French people when they obtained independence. Their god turned out not to be God, but the God of Reason, who/what later became their official god. It was state-sponsored atheism. There are three isms pertaining to the divine - theism, deism, and atheism. Theism is the truthful God, Deism uses partial truth; they have a god but a false one, and atheism claims no god. At least atheism is an honest belief! Deism proclaims God then makes Him powerless and impersonal. At least the French were honest - in their cult of reason, they made their god Reason!