Prepositional phrases are fixed groups of words that function as a preposition and establish semantic relationships between terms in the clause. They can indicate conformity, cause, substitution, place, position, purpose, time, or reference, linking a complement to another element of the sentence. To recognize their use, it is important to relate them to the functions already seen in Prepositions and to the notions of Common Prepositions.

According to expresses conformity with a rule, information or plan, while por causa de introduces the cause of a fact or situation. The former tends to appear in formal and administrative contexts; the latter is very common in everyday speech and ordinary writing. Both link a main term to a complement that explains the basis or reason for the action.

IdeiaIdea.	ExemploExample.
De acordo com indica conformidade.According to indicates conformity.	De acordo com o plano, a reunião será amanhã.According to the plan, the meeting will be tomorrow.
Por causa de indica causa.Por causa de indicates cause.	O evento foi cancelado por causa da chuva.The event was canceled because of the rain.
De acordo com introduz uma fonte ou orientação.According to introduces a source or guidance.	De acordo com a professora, a prova mudou.According to the teacher, the exam changed.

Instead of expressing substitution and showing that an element occupies the place of another, whether in choices, actions, or preferences. Beside \"de\" and \"junto a\" indicate physical proximity, while \"em frente a\" and \"à frente de\" mark a preceding or opposite position, with regional variation in some uses. In these cases, the locution may contain contracted articles, such as \"em frente ao\" or \"ao lado da\", depending on the following word.

IdeiaIdea.	ExemploExample.
Em vez de indica substituição.Em vez de indicates substitution.	Em vez de chá, tome café.Have coffee instead of tea.
Ao lado de indica proximidade.Ao lado de indicates proximity.	O banco fica ao lado do mercado.The bank is next to the market.
Em frente a indica posição oposta.In front of indicates an opposite position.	A escola fica em frente ao parque.The school is in front of the park.

A fim de is a more formal locution that indicates purpose, and is normally followed by an infinitive verb; para can also indicate purpose, but it is more common and more colloquial. Antes de and depois de establish temporal relations and show precedence or succession with respect to another event. These locutions help to organize intentions and the sequence of actions with precision.

IdeiaIdea.	ExemploExample.
A fim de indica finalidade formal.A fim de indicates formal purpose.	Estudou a fim de melhorar o português.He studied in order to improve his Portuguese.
Para indica finalidade mais comum.Para indicates a more common purpose.	Saiu cedo para evitar o trânsito.Left early to avoid traffic.
Antes de indica anterioridade temporal.Before indicates temporal anteriority.	Antes de sair, fechou a janela.Before leaving, he closed the window.

With regard to and with respect to introduce the topic being discussed and serve to resume a subject or open a new reference. These locutions tend to appear with stressed pronouns, such as me, you, us, and you all, especially after de, por, and a respeito de. When the structure requires an article, internal contractions also occur, such as de + o forming do, and de + a forming da.

IdeiaIdea.	ExemploExample.
Com relação a introduz o tema tratado.With regard to, it introduces the topic addressed.	Com relação ao projeto, houve mudanças.With regard to the project, there were changes.
A respeito de retoma um assunto.With respect to, it resumes a topic.	A respeito de nós, nada foi decidido.With regard to us, nothing was decided.
Pronomes tônicos podem aparecer após a locução.Stressed pronouns may appear after the locution.	Falaram por causa de mim com respeito.They spoke about me with respect.

Prepositional phrases function as stable units that connect terms and specify sense relations with great precision. Their correct use depends on the function they perform in the sentence, the register required, and the internal contractions caused by the articles and pronouns that accompany them. In well-constructed texts and speech, they allow indicating conformity, cause, substitution, place, purpose, time, and reference with naturalness.