Why can't a king take a pawn or other piece if that piece cannot legally move?

I was in a game, I thought that chess rules state you cannot intentionally put your king in check, but in the case where taking the piece with the resulting take on the king would put the opponents king in check, why is that not legal as a move. In other words, the king by definition is not in check until the black king moves out of the way but when that happens, you just move the king out of the way.

example:

White positions:

kh2, g2, f3

Black:

kf4, ra2

Black to move.

 (I tried to upload a PGN but I cannot figure out how, I'm not exactly the brightest light bulb in the room)

King cannot take on f3 as it appears he is placing himself in check, but how? g2 cannot itself take the king as it would place the white king in check. Seems like a bit of a conundrum to me but perhaps this is covered somewhere in the rules.

(Off topic, can someone point me to a link where I create and upload a PGN).

FX

A King cannot place itself in check, so the capture on f3 is illegal.

This question comes up every so often.

Notice it's a contradiction: "I should be able to place my king in check, because the opponent can't place their king in check"

No. Because the rules apply to both players

It can be thought of as whoever takes the other player's king first wins; normally, if the king was not on f3 and instead a bishop was there, imagine from white's perspective that he would not take the bishop because he would lose his king and therefore the game; however, if a king is there, then he will open his king to capture, but he still will take the opponent's king first and thus he is the winner. Just a way to think about it though of course opening a king to check is always illegal

in post #2, black has no worries, pretty much an automatic win anyways from there....

 In this case, taking on f3 cannot result in a capture since that puts the opponents king in check.

Yes, you are 100% correct, I could not take on f3, but it still seems like a bit of a paradox.

To set up a position, simply click on the the chessboard icon at the top left of your comment window.

To create a PGN, the simplest was is to download the freeware (and extremely excellent analysis or play vs engines program) Lucas Chess (https://lucaschess.pythonanywhere.com/) find the "Create Your Own Game" in one of the top menu selections, then save it as a PGN file.

To put it in a chess.com comment, open the PGN file in a text file reader (Notepad in Windows), copy and paste it into the "Load PGN" section of the window you get from the same chessboard icon mentioned above.  You can use the Set Up Position sub-window to flip the board if you want Black at the bottom.

Thanks for that valuable information :-)

FX

Yes, I won, when I was thinking about how to continue, I thought I'd take the pawn with my King to see if the board would let me. Obviously no, but since I am pretty much a newbie, I was just curious since the rules don't really tell me whether it is legal or not. I maintain it is a paradox (which exist in any rules based system).

FX

It's not a paradox. You can't put yourself in check because that would result in the "capture" of the king.  Think of it this way:

... Kxf3 - gxf3 Rxh2

In the hypothetical line I just gave (it's hypothetical because we don't capture kings in chess, hence you can't self-check), black's king gets captured first, so it doesn't matter that white self-checks while capturing the enemy king. Rxh2 can't be played anyways since the black king is already "captured".

The pawn cannot capture the king after kxf3, because that puts the white king in check. If the we see something like kh3 then simply rxg2. Black king is no longer in jeopardy and white has lost another pawn. The point is that the rules are not specific, you cannot put your king in check on a move, it does not say anything with regards to this sequence. I maintain that according to the rules, kf3 is not really check to the black king (though white is pretty clearly lost). Check means there is a threat to take the king, in this specific position, the king cannot be taken.

Did I not see this position in a puzzle somewhere?

you are wrong. please play tic tac toe instead, it fits you

Think of it as this way...

The first person to capture the king wins, and when the king is captured (not really captured but whtevr) the other pieces are rendered useless. So then if the person whose king was 'captured' (if dat is possible) cannot capture the other king...

 It is a game of non-realtime tempo and white starts out 1 tempo ahead of black. 

PG explanation:  Since the black king has been CAPTURED, the war is immediately over and the royal leader then surrenders his kingdom, his army and all of his assets to the conquering enemy side.  The black rook that was preparing to capture the white king is now recruited as an enlisted member of team white. 

A colorful medieval wartime scenario:  (Rated PG-13)

       In a large open field dividing two kingdoms, an eerie silence has settled in, but in his head still rings the sounds of agonized screams and metal slicing flesh.  His royal garments have been stained by at least 9 different shades of red.  Intoxicated by a mixed cocktail of emotions, he nears the conclusion of a violent and arduous struggle.  The fatigued yet determined black monarch, Kevin, marches deeper into enemy territory at a rigid pace. With death in every direction, he is tormented by the perturbed energy of anxious souls that have been abruptly ripped from their mortal chambers. In his head, a playlist of visions from each of his men's final moments are stuck on a shuffled replay.  The dying faces haunting his memory are following seemingly scripted emotions: surprise and shock, followed by a chilling fear, and then finally displaying a hint of somber acceptance as their fleeting spirit renders them limp.   He carries on, there is no turning back.  He is on an autopilot mission towards his unfinished destiny.   Stepping over scattered body parts and through puddles of blood, the stubborn leader draws his sword as he boldly approaches what is left of his adversaries.  He gives the signal to his sole surviving warrior, a chariot marksman named Rory, to prepare for a final engagement. 

       Geoffry, 19, and Finkledern, 17, were just amateur bodyguards, fresh out of the academy.  Before the sun rose on that day they were no more than timid virgins of combat, but the events that took place on that battlefield had forged them into something else, their old identities left on the ground, as deceased as their fallen comrades.  Broken down and rebuilt they were now essential cogs in the nation's war effort. The only departure from that battlefield they would accept was an entire transformation of either body or spirit.

         As King Kevin approached, the two stone-faced bodyguards stood their ground, loyal to their duties.  King Kevin and the seemingly-confident guard met gazes.   As the bloodthirsty dauntless eyes of the tenacious ruler penetrated the young warrior's soul, Finkledern felt his mortality for a brief moment before the  aberrant enemy became a blur in his peripheral.  Finkledern knew that he was now completely powerless to defend himself from this angle, and he would have to rely on the protection-chain system that they learned at the academy and trust in King Kevin's fear of his own mortality.
Finkledern could  hear the crunch of King Kevin's armored boots approaching closer and closer, slower and slower.  "Did the footstep stop?"  Why did they stop??"  "Was Geoffry still defending me??"  Finkledern knew something wasn't right.  Finkledern's heartrate began to skyrocket, all of his suppressed emotions were now flooding back in.  He wasn't supposed to be afraid, he knew from his training that if he followed the rulebook, and kept his post, he should be safe from the enemy king, but he was paralyzed by a devastating fear.  He could feel what was coming yet still he did not budge. King Kevin poised himself to strike, and Finkeldern knew it wasn't a bluff.  This was his calling, his duty, and his final chapter.  Accepting of his fate, Finkledern began to relax, time slowed down nearly to a halt, and in this lasting moment of silence he had peace.  He knew he would live on as a martyr, a legend. He inhaled a chest full of crisp air, closed his eyes, and a cracked a smile as he slowly breathed out.
        In an instant, a crushingly tight pinch yanked Finkledern's neck.  He opened his eyes and clenched his hands over his freshly-permeated carotid artery.  He fought against his instincts to panic, but he couldn't breathe.   Kevin withdrew his sword and stood there watching his hapless victim.  Finkledern felt like he was drowning and being choked at the same time, but it wasn't as painful as he thought it would be.  His body violently attempted to cough as blood filled his lungs.   He collapsed to his knees with his hands still firmly on his neck, turning towards King Kevin, blood spraying out with every heart beat.  King Kevin and Finkledern shared this one last moment locking eyes.  Finkledern then managed a small smile as he saw Geoffry's pike skewering King Kevin's head from behind like a shish kebab

      Fearless King Kevin died with no regrets.  He never had the chance to realize his own mistake, because his memory, and his mechanics to receive and process data had been rapidly reorganized in a less-than-functional manner.
King Kevin made the fatal assumption that the bodyguard Geoffry was pinned to his duties of protecting his own king from the threat of Rory.  Unbeknownst to King Kevin, when Rory saw simultaneously an open shot on the white king AND his own fallen leader, he thought about his wife and kids at home, and the fact that King Kevin was a d**k to him anyway, and so he choose to surrender and join the other side.
THE END.

Haha.

Starring:
King Kevin (king on f4)
Finkledern (brave pawn on f3)
Geoffry (honorable g2 pawn)
Rory (rook on a2)


notable mention:
White king on h2

The way I understood it when I was learning (... Kxf3 ; g2xKf3) and without a king, all of black's other pieces are automatically removed from the board, leaving the white king a winner by knockout.