Ed is correct: the first sentence is correct and the second is not a proper sentence (it's meaningless). In writing the sentence one should not split the infinitive "to jump", although to not jump it is used often in speech. So, if we don't split the infinitive, the first sentence would be "I decided not to jump". Here are a few more examples of infinitives that are not split: - I prefer not to go. - Do you not want to go? - I hope not to be chosen. Look at this website for a good explanation of split infinitives: http://english.stackexchange.com/questions/23152/order-of-not-with-infinitive

The first is right, the second wrong. You must have the "to". "Decide" needs to be followed by an infinitive if followed by a verb.

Deux verbes qui se suivent le deuxième se met à l'infinitif c'est comme en français , je pense.

Hello Kamenko! Thank you very much :)

I decided not TO participate here as an English speaking person, but I would like to say hello to my friend Li.