Commentary for Genesis 48:18

לא כן אבי, I did not do as you thought but placed my firstborn on your right and the younger one on your left. Yaakov replied that he was aware of this (verse 19) because “I know that you are a wise man and would see to it that your sons had been placed in the manner in which you intended them to receive their blessings. However, I plan to bless the younger one who is on your right with my right hand and I withdrew my left hand from his head in order to be able to do this.” להסיר אותה מעל ראש אפרים, and to transfer it (my left hand) to על ראש מנשה, to the head of Menashe. Whenever the verb הסר appears it is written in a sort of abbreviated syntax, the predicate which is supposed to follow it or precede it being omitted. Some examples are: Judges 4,18 סורה אלי אל תירא, the meaning being סורה משם לפנות אלי, “turn away from there in order to turn towards me.” A similar example of this is found in Genesis 19,3 ויסורו אליו, where the precedingמשם לבא, “from there in order to come” is omitted and the reader has to fill it in by understanding the context .

כי זה הבכור. שים נא ידך על ראשו. Once he would place his hand on the head of Menashe, Joseph felt sure that his father’s mind would follow the direction of his hand. This has been illustrated in Numbers 27,23 when Moses placed his hands on Joshua when appointing him as his successor. [if the physical contact would not be of significance, why would Moses have bothered? Ed.] The right hand is presumed to be stronger than the left, hence a blessing conveyed by means of the right hand would be a stronger, more comprehensive blessing.

ויאמר יוסף..לא כן אבי, Joseph said to his father: "not so my father, etc." We need to understand why Joseph did not simply say: "this one is the firstborn," instead of the preamble "not so my father."

לא כן, “not so,” some people claim that Joseph certainly did not say to his father outright that he had not acted correctly, but that the words meant that he, Joseph, had been mistaken when he had thought that his father had erred. Nonetheless, Joseph told his father that he preferred for him to place his right hand on the firstborn Menashe.

לא כן אבי, “not so my father!” He meant: “they are not lined up in the order that you thought they were lined up.”

Joseph entertained two possible doubts. 1) Inasmuch as Joseph and his sons were facing Jacob, and it was customary for Joseph to have his firstborn on his right and the younger one on his left, they would appear in the reverse position when viewed from Jacob's vantage point. Jacob may therefore have reasoned that in order to place his right hand on the older one of the two he had to cross his hands. 2) On the other hand, Joseph reasoned that it was possible that his father crossed his hands in order to place his right hand on the head of Ephrayim, deliberately, thus giving him preference over Menashe. In view of this Joseph first told his father that if he had assumed that Joseph had placed the boys as he usually did, i.e. Menashe on his right, לא כן אבי, i.e. he did not do so this time. If, on the other hand, Jacob had deliberately placed his right hand on the head of Ephrayim, Joseph registered his protest by saying: "place your right hand on him for he is the firstborn." He wanted to know why his father denied his firstborn what he thought he was entitled to.