doctor's advice

[navi tasan]

1-You should not receive a blow to the head. If you do, your eyesight might be damaged.
2-You must not receive a blow to the head. If you do, your eyesight might be damaged.
3-You are not to receive a blow to the head. If you do, your eyesight might be damaged.

Which sentences are acceptable if the context is that of a doctor talking to a patient. In other words, the sentences are not supposed to express commands. The person to whom they are addressed is not "answerable" to the person uttering them but has to abide by them for his own sake.

[curates-egg]

1-You should not receive a blow to the head. If you do, your eyesight might be damaged.
2-You must not receive a blow to the head. If you do, your eyesight might be damaged.
3-You are not to receive a blow to the head. If you do, your eyesight might be damaged.

Which sentences are acceptable if the context is that of a doctor talking to a patient. In other words, the sentences are not supposed to express commands. The person to whom they are addressed is not "answerable" to the person uttering them but has to abide by them for his own sake.

All of the sentences are highly unlikely. Nobody chooses to have a blow to the head, and so nobody is likely to be told that they should/must not receive a blow. A doctor is more likely to say something like, "You must protect your head from any possibility of bumps or knocks."

[navi tasan]

Thank you Curates-egg.

What do you think of these:

A-When you play football, the ball should not hit your head.
B-When you play football, the ball must not hit your head.
C-When you play football, the ball is not to hit your head.

[riquecohen]

Thank you Curates-egg.

What do you think of these:

A-When you play football, the ball should not hit your head.
B-When you play football, the ball must not hit your head.
C-When you play football, the ball is not to hit your head.

Curates-egg's response in post# 2 is applicable here as well. The only modification I would make to that response is to change "bumps or knocks" to "blows or trauma," which is more likely in AmE.

[Raymott]

Thank you Curates-egg.

What do you think of these:

A-When you play football, the ball should not hit your head.
B-When you play football, the ball must not hit your head.
C-When you play football, the ball is not to hit your head.

If this is the case, the doctor is more likely to say:
You should not play football.
You must not play football.
You are not to play football.