Which is correct: in depth or in depth.

Context helps to understand the difference. But not always.

Distinguishing between an adverb  in depth and a noun with a preposition in depth is often difficult. As with many things, context plays a big role here.

If from the predicate you can ask a question about the circumstance of this word, then we have an adverb with a spatial or temporal meaning, which is written together. For example: Spread (how?) in depth and breadth. The problem was not solved, but driven (where?) deeper.

Another case is a combination of a preposition and a noun that controls another noun. For example: dive into the depths of the sea, delve into the depths of the problem . As a rule, you can insert a dependent word between them: dive into the depths of the sea , delve into the very depths of the problem.

At the same time, sometimes the word in depth acts as a preposition. But since in modern Russian this preposition is still in the stage of formation and the difference between it and the combination of a noun with the preposition deep is difficult to grasp, a variable spelling is possible: dive deep into the ocean, go deep into the forest . In such cases, you can decide whether to write together or separately, depending on your understanding of the text.

Subscribe to a free writing course from the editors of ProPedia “ Initial ” and the Telegram channel of the same name to become more literate and create good texts.