A grammar issue I've just tuned in to – or into?

The long-awaited and much-postponed dinner with friends had finally come off, after months of rescheduling. And at some point between the main course and the dessert, conversation somehow turned, as sometimes happens at a wordsmith’s dinner party, to issues of grammar. 

OK, one of my guests began, we all know the difference between in and into. But what about the difference between into and in to?

Hmm, funny you should ask – I’ve been meaning to research this one.

We use into “to indicate movement toward the inside of a place,” as the late Jane Straus wrote on her Grammar Book blog. “In to is the adverb in followed by the preposition to.”

The in/into distinction is straightforward: “He first moved into the city 10 years ago, and he’s been living in my neighborhood for the past five.”

But the in to/into distinction is trickier. To get it right, be clear on what your verb is. If it’s phrasal, you probably should stick with “in to” rather than “closing it up,” as editors say.

What’s a phrasal verb? It’s one made up of a verb plus an adverb or preposition. English is full of phrasal verbs: come in, go out, get on, get off, get across. They’re often idiomatic. That is, they are “established by usage as having a meaning not deducible from the meanings of the individual words,” as the Oxford English Dictionary puts it. Websites for English learners abound with lists of them, with definitions.

For example: “He turned his paper in to his teacher.” The verb is “turn in,” meaning “to deliver,” and so you need “in to,” not “into.” But there’s also an idiom “to turn into (something),” meaning “to be changed or transformed”: “He turned into a fine young man once he’d grown up.” That one takes “into.”

You might write in to your congressman, but an editor will sometimes write into a reporter’s story material from a wire service.

The close-up question also arises with log in and log on. (Some purist techies insist that log in is correct only with reference to Linux systems, but I think that distinction is lost on the masses, including the techie masses.)

Both “log” verbs can easily be seen as phrasal, and therefore requiring “in to” or “on to,” respectively: I logged in to my account.

Here’s how Ms. Straus put it in an exchange with a reader on this subject: “The real question to ask is, ‘Is there actual entrance?’ If so, use ‘into.’ ”

But somewhat later she opined, “ ‘Into’ implies entrance, which one could say is meant figuratively here, even if not literally. Therefore, I would ... say that either into or in to is acceptable.”

What about “tune in”? It’s clearly a phrasal verb. But here are some usage examples from Oxford Dictionaries: “you must tune into the needs of loved ones” (illustrating tune in) and then, to illustrate be tuned in: “it’s important to be tuned in to your child’s needs.”

We have “into” with one, and “in to” with the other. What’s up with that? Is it the distinction between the action of tuning in and the state of being tuned in that matters? Perhaps. That would be analogous to the earlier example of moving into/living in.

However much we long for clear-cut rules, some of these questions may have more than one reasonable answer. 

And we nitpickers may just have to live with that.