'To swiftly go' or 'to go swiftly'? [duplicate]

Possible Duplicate:
Are split infinitives grammatically incorrect, or are they valid constructs?

One of my friends once told me 'to go' is considered a whole word and no word should be put in between. Are either grammatically incorrect and is one preferred?

No, what you're witnessing is essentially a spurious prescriptivist argument.

The argument (more of a non sequitur) goes something like this: (a) in Latin, the infinitive consisted of a single word (e.g. "ire"); (b) in English, the 'infinitive' consists of two words, e.g. "to go"; ergo, in English, we 'should' not put a word in between the two 'parts of the infinitive'.

Now, if you want to subscribe to this etiquette, then by all means do. But there's no inherent necessity to do so. And the argumentation behind it is totally spurious.

In reality, all evidence points to the infinitive in English being e.g. the single word "go"; the fact that you often need another word alongside it to produce the semantic equivalent of a Latin infinitive is simply a translation problem, not a satisfactory analysis of the structure of the language per se (actually, a Latin infinitive may well sometimes be translated using a completely different entity, e.g. an -ing form).

It's well observed across languages that infinitives, in some constructions, are specified or 'introduced' using a word with a 'special' status, often the same superficially as a preposition. For example, German has "zu" and French has "de". These are sometimes called "Pre-Infinitival Prepositions" (PIPs) and may be analysed e.g. as a complementiser (but different analyses have been proposed).

And it's well observed across languages that the infinitive and its PIP can be separated by other words. For some reason, people got on their high horses about this in English, but it's perfectly common and uncontroversial to have e.g. in French "de bien le lui donner", where the PIP "de" and the infinitive "donner" are separated by no less than 3 items. And French, unlike English, is actually derived from Latin for goodness' sake!

Consider also that the so-called "split infinitive" may be the only reasonable choice in some cases. For example, consider these:

He failed completely to understand.

He failed to completely understand.

He failed to understand completely.

Only the middle version of these-- the so-called "split infinitive" version-- is unambiguous in the scope of 'completely'; the interpretation of the other two versions is ambiguous as to whether it was the failure or the understanding that was complete.

Or put another way: write in a way that sounds clear, natural and intuitive to you, and don't invent spurious problems where they don't exist.

Neither is incorrect. Many generations of schoolmarms have inveighed against splitting infinitives (that's what you're doing with "to swiftly go"), but it's strictly a stylistic choice: Oxford Dictionary's Take. As the link states, some folks get all bent out of shape about it, but if it works better in the writing, go for it.

As for the "Latin objection" to it...you can't split an infinitive in Latin because it's an inflected language - the infinitive form is created by adding "-re" to the stem, e.g., gusta, "taste" plus "re" = "gustare" - to taste. English ain't inflected (much).

"To go" is not considered a single word, though it is a single language unit (called an infinitive). Though it is considered by some to be bad form to interpose an adverb between the infinitive "to" and the infinitive verb (this is called a split infinitive), it is a matter of personal preference, not grammatical correctness. Someone who does not know the language well should probably use to go swiftly, since it is universally acceptable.