We are faced with two expressions that, in sound terms, are identical, however, present differences in applicability, in view of also different communicative circumstances. For this reason, let us analyze them in a particular way.
The one that first appears in the title is constituted by the hyphen, as well as representing a compound noun whose semantic meaning refers to everyday, morphologically saying. In terms of syntax, it can occupy different positions, sometimes representing a subject, sometimes a direct object, and even an adnominal adjunct. Therefore, let us verify such cases through the following examples:
the day to day of some workers is hard.
In this case, the highlighted term represents the subject of the clause.
I consider the day by day rather monotonous.
In this context, it occupies the function of a direct object, since it completes the meaning of the verb to consider – this being a direct transitive (What do I consider? The day by day)
Those specific outfits are intended for use in the day by day.
We found that it is an adnominal adjunct.
If you haven't noticed, you should pay attention to an extremely relevant fact: the term, which was previously spelled with a hyphen, has been abolished in all the examples in question. This fact stems from the new rules arising from the Orthographic Reform, which has been in force since January 1, 2009.
According to this, compound words that have a connecting element between their terms (represented by a preposition, article or pronoun) no longer require the use of the hyphen. In addition to the expression under study (day-to-day), there are still others, such as peo de tomboy, honeymoon, carne de sol, weekend, etc.
However, some exceptions tend to manifest themselves, as is the case of eau-de-cologne, more-than-perfect, nest egg; some names of botanical and zoological species, such as bem-te-vi, sugarcane, joão-de-barro; and some homeland adjectives derived from compound toponyms, such as mato-grossense-do-sul, among others.
In terms of this aspect, there is a factor worth mentioning: until the year 2012 the old spellings will still be accepted, that is, we have until that date to learn the new spellings. However, the sooner we try to establish familiarity with these, the better we will perform as users of the language system.
Let us turn our attention to the term “day to day” which, regardless of any details, has always been spelled without a hyphen. He, in turn, represents an adverbial phrase, whose meaning is "every day", "daily". According to the syntactic function, we say that it is classified as an adverbial adjunct, whose purpose is to indicate the circumstance expressed by the verb, the adjective or the adverb itself. Therefore, let us analyze some representative cases:
The wave of violence that devastates contemporary society is growing day by day. (daily)
It is inferred that this expression modifies the verb to grow (grow).
He is more interested day by day. (daily)
We found that the attribution is now given to the adjective “interested”.
By Vânia Duarte
Graduated in Letters
Brazil School Team
A or is there? - When should I use these terms? Click on the link and clarify your question!
Grammar - Brazil School
Source: Brazil School - https://brasilescola.uol.com.br/gramatica/dia-a-dia-ou-dia-dia.htm