The idea of split infinitives, largely taught during the mid-20th century, can harm the clarity of sentences — and is mistaken about what an infinitive is in the first place.

When you look up a verb in the dictionary you find the infinitive form.‎ In English it’s made up of two words: to swim. ‎ But in French it’s just one, nager. ‎ And if you want to say something more ...

The infinitive is the basic, unconjugated form of a verb. It is the ‘to’ form of a verb in English. An example of an infinitive in French is jouer (to play).