Editing Mesechtas Terumot (section)

==== The Knowledge of the Person Affects the Object ====
The Rebbe explains that according to the Jerusalem Talmud and the Rambam's ruling, Rabbi Akiva's reasoning represents a third approach to the nature of a dry-in-dry mixture. According to Rabbi Yehoshua, the entire definition of the mixture depends solely on the person's knowledge and thought, but Rabbi Akiva holds that although the foundation of a dry-in-dry mixture is based on the person's knowledge and thought, the state of the person's knowledge affects the actual physical object. This is the Torah's innovation regarding the law of dry-in-dry mixtures: even though from the perspective of reality itself, the prohibited item is not actually mixed with the permitted one but merely cannot be distinguished on its own, and therefore the foundation of the mixture's definition is based on the state of the person's knowledge, this state of knowledge causes a change in the reality of the object, as if they were actually mixed.

Therefore, the application of the laws of mixtures based on a person's knowledge only applies when one did not know at the time of the falling; then we say that the mixture that exists in the person's knowledge causes the application of the laws of mixtures, as if it fell into one hundred. But when at the time of falling one knew, meaning that in the person's mind the black and white figs were not mixed, the subsequent forgetfulness cannot create something new in the figs, since from the perspective of the figs themselves, the white and black ones are not mixed, and forgetfulness cannot uproot this reality (nor can it uproot the person's knowledge at the time of falling, when he knew whether a black or white fig fell).

In other words: For a person's knowledge to effect a law in the physical object, the black and white figs, which are not mixed in their essential nature, there needs to be a change in the figs themselves, '''that fell''' either black or white, whereby a mixture is created in reality, as the black fig is among the black ones. Then, when it is not known which of them fell, the mixture in the person's mind creates a mixture in the figs into which a fig of terumah fell. But when one knew and forgot, the person's forgetfulness does not mix the figs that in reality are not mixed.

The Rebbe explains the reason this concept, that a person's knowledge and thought can affect something outside of himself, is specified regarding terumah specifically - because the fundamental law that thought has effect is expressed regarding terumah, as learned from the verse "And your terumah shall be reckoned unto you as the corn from the threshing floor," from which we learn that terumah can be designated by thought alone. And although this case is not discussing the law of separating and sanctifying terumah but the law of its nullification, whereby the figs become permitted for consumption, nevertheless this stems from the fact that in the laws of terumah, a person's thought has special power.