That's my point Mick. Any challenge for the ball asks for there to be a decision or judgement from the referee - the first being was it fair?
What is fair is largely defined by the LOTG, however, I still believe that a player can commit a foul without making contact with the opponent. Attempting to tackle isn't an offence as such, but any tackle needs to be judged by the referee. THe LOTG don't define a 'tackle' as such, but an attempt to win the ball is pretty accurate, or a 'challenging an opponent for the ball' to borrow from Law 11.
So for the sake of argument, can we assume that a 'tackle' is a challenge for the ball while it is on the ground/below knee level and that we are only having to consider the feet and legs of the players - let's not bring arms and shoulders etc into the example.
So, can a player challenge unfairly, without touching the ball or the opponent?
He can win the ball cleanly, with or without contact. Contact doesn't mean it's a foul - Play
He can impede an opponent's progress without physical contact - IDFK (under certain circumstances)
He can win the ball with a careless challenge, which has introduced some risk to his opponent. - DFK
He can win the ball recklessly, where there is a clear risk of injury to the opponent. DFK-YC
He can win the ball with an excessive challenge, where he has used excessive force. DFK-RC
He can, jump in, both feet raised, studs showing, over the top of the ball with a stamping motion and miss both the player and the ball because his opponent sees it coming and avoids it. Contact or not, he is walking.
It is the fact that he has challenged an opponent for the ball that brings it into the realm of possible foul. The specific offence could be one of a number.
So sliding in to a challenge, missing the ball and the opponent loses his footing while attempting to avoid possible injury by jumping over the leg, stumbling and falling over. The fact that the challenger has introduced an element of risk to his opponent's safety that makes it a foul, and that is what we need to judge. Not whether contact is made or not.
The challenger may miss the ball, but in doing so has caused the attacker to change direction to avoid contact and the ball goes to a defenders team mate, that otherwise would have remained in the attacker's possession. Have the defending team won the ball fairly or not?
It is impossible to hypotheticalise (is that a word?) real-world situations in a forum such as this, but the question can a foul tackle occur if there is no contact made with the ball or the opponent? Has to be answered 'Yes - in certain circumstances'