While studying Japanese I came across some grammar that really confuses me:
ここから、始まってはいけない
Ok, it says 'you must not start from here', which seems agreeable because the sentence is in a negative form. However then this sentence appears:
ここから、始まらなくてはいけない
Which roughly translates to 'you must start from here'. Why is this sentence also negative? Why are 'must' and 'must not' both written in a negative form and how can I tell them apart?