First, I doubt that any Calvinist uses logic as the basis for all that he believes. I think you overstated the case.
Actually, if what you began learning wasn't logical - would you have continued in it? I seriously doubt it, and nor would anyone else. Proper deduction and reasoning within logic allows for us to grasp and have cohesive understanding.
You are confusing the issue of whether God has foreknowledge of events with the question of on what basis He determines what will happen. God does foreknow everything that will happen because He has decreed that it will happen. God did not decree that things would happen because He already knew that they were going to happen. That just doesn't even make sense
Actually, it does make ALOT of sense, just not to someone who will not see.
But let me show you something first, if I may:
You state:
God does foreknow everything that will happen because He has decreed that it will happen
Now within this construct we have a multitute of problems.
1. Man does not choose sin or fall and thereby bring condemation upon himself. Why? Because God decreed from the outset who will be condemed and by His decree they will fall into sin and not ever know Him. Ergo, He punishes those He fully intended to never know Him and thereby reject Him.
1 (a). IF God decrees and THEREFORE due to this already knows the outcome - you have succefully established double predestination which is a blatant heresy. As He does not FORSEE mans decision to reject Him, we have God making the decision for him and man just did as he was created to do - be condemed to hell before any are chosen. Then He only chooses SOME to show love to out of this group by which He created for the purpose destruction.
2. If God decrees man will fall, it IS NOT man that has chosen rebellion but that which was decreed he does (this includes Adams fall). Now we have mankind simply followin along (sorry, but robot analogy included here) doing what God decreed he WILL do (specifically Adam) and had no choice but to do what God created him to do. Now we have God being the author of sin. Why? Because God is the first cause of all things including sin.
2 (b). Now we just just impuned Gods righteousness, tainted His Holiness, and absolved God's love. For if God so decreed first - By the very nature of the statement He would then be the very author of sin and a partisipator of it. We, due to this same statement have God decreeing mankind to fall into sin and then giving this same creation who is doing what they were decreed to do - everlasting torment for being who He made them to be. [Unrigheous] Thereby tainting His Holiness for He would not be seperated from ungodliness being the very creator of it [Unholy] And since SOME where choosen for Heaven and many more for eternal torment by there very creator -
I have YET to hear a defencable view within Calvinism that does not make God the very author of sin. God will not tempt man TO sin nor does God cause man to sin.
Now what is most funny is I beleive the Calvinist has and hold the same truths I do, but our views as to the mechanics of their operation differ. We have differing VIEWS about the same immutable truths. This is just an area I don't agree with since it is mostly speculation anyway!