Let's say a person's name consists of 3 words (e.g., Jhonatan Christian Maraschin). Is the middle word (e.g., Christian) second given name (Jhonatan Christian // Maraschin) or first surname (Jhonatan // Christian Maraschin)? If it can be both, how can I tell? Or is it just a "middle name" like in English?
In Brazil it can be either.
It's not unusual for parents to chose only one surname for their child, usually the father's surname. How can you tell, then, if a middle word is part of one's surname? You can't, unless you know most given names and most surnames here. Even so, sometimes you'll find a surname that looks like a given name, and vice-versa.
Examples where the second name is likely to be part of the first name:
- Maria da Luz Ferreira
- Fernando Antonio da Silva Santos
- José Antonio de Castro
- Ana Carolina de Assis
Examples where the second name is likely to be a surname:
- Roberto Soares de Souza
- Alexandre Martins do Couto
- Teresa Freitas da Silveira
- Natália Siqueira Ribeiro
Given names that look like surnames:
- Santiago Pereira de Santana
- Miranda de Oliveira Guimarães
- Valentim José de Almeida
Surnames that look like a first name:
- Roberta Pedro Guimarães
- Antonio Rosa da Silva
- Renato da Conceição Menezes
- Teresa de Fátima Gabriel
It can be both. You generally can tell because most given names and surnames are distinct. Sometimes the two groups of names are separated by de or dos (though de can also be used to unite two words of a name consisting of several words, such as Maria da Piedade). In Portugal, by far the most common is to give babies two first names and two surnames, though it can be as low as one surname as high as four. Some people are also given only one first name. When there are two surnames, the last name is usually the father's. Upon marriage, many women — but not as many as in the past — append the husband's last surname, so they get three surnames.
In Portugal, the middle word in a name with 3 words will be a first surname.
Usually, people get one or two first names and then two or four family names.
They get family name from the mother's side, and family name from the father's side.
Because names are long, usually a short form is adopted with one of the first names and one of the family names:
- Antero (Tarquínio) de Quental;
- Fernando (António Nogueira) Pessoa;
- António (Luís Santos da) Costa;
- Paulo (Sacadura Cabral) Portas.
Note that the last name is the one usually picked.
This is because the father's family name comes after the mother's family name.
In contrast, in Spain the first family name is usually picked, and the father's family name comes before the mother's family name:
- Miguel de Cervantes (Saavedra);
- Arturo Pérez-Reverte (Gutiérrez);
- Miguel de Unamuno (y Jugo);
- Rosa Montero (Gayo);
- Elvira Navarro (Ponferrada).
When someone had no known father, they would get their mother's family name only:
- [Flor Bela d'Alma] [da Conceição] was the daughter of Antónia da Conceição Lobo and João Maria Espanca; she got her mother's maternal family name only, and a rather long given name. (She would posthumously become Florbela Espanca, when her father assumed paternity.)
But since 1977 this is not allowed by the Portuguese law, according to the Portuguese Bar (of Lawyers):
A lei portuguesa não admite a existência de crianças com pai incógnito desde 1977
If the name is longer, you will need to recognize it yourself - which are given names and which are family names.
Most people have 4 or more names, but it's not uncommon for someone to have only 3 names:
- José (de Sousa) Saramago;
- Paulo Coelho de Souza;
- Agustina Bessa-Luís.
Very often people have up to six names (family name in italics for your convenience):
- José Sócrates Carvalho Pinto de Sousa;
- Pedro (Manuel Mamede) Passos Coelho;
- Mário (Alberto Nobre Lopes) Soares.
People with ties to nobility and royal houses will often keep very long family names, sometimes using hyphenation:
There are actually four different things.
- Maternal surnames, such as
José Nóbrega da Silva.
- Second given names, such as
Ana Carla Pereira.
- The first part of a composite paternal surname, like
Augusto Castelo Branco
- The second part of a composite given name, as in
Maria do Rosário Pereira.
It is necessary to know these lexical entries one by one. Generally, surnames are different from given names, and it is possible to have some loose guidelines: names of animals, trees, cities, professions, are quite certainly surnames (Coelho, Raposo, Tourinho; Pereira, Nogueira, Figueira; Coimbra, Santarém, Lisboa; Cardador, Pastor), as well as ancient patronymics turned surnames (Henriques, Bernardes, Fernandes). But there is overlap, as pointed in other answer. Composite surnames sometimes make sense (Castelo Branco, Índio do Brasil), but not always (Monteiro Lobato, Mena Barreto). Composite names are mostly the various aspects of the Virgin Mary: Maria das Dores, Maria do Socorro, Maria da Conceição; another possibility is the name of historic characters (Paulo de Tarso, Rui Barbosa, Washington Luís). Again there is overlap; Socorro is not a common surname, if at all, but Conceição or Rosário are. In general, you can be sure that the first name is a given name, and the last one is the paternal surname (unless it is a familial descriptor, such as Filho, Neto, Sobrinho, Júnior). Middle names are more complicated; usually native speakers know which is what, but there can be difficult cases even for us. They usually become clear if we know the parents' names.
Complementing Centaurus answer, let me remark that very often only the first and last names are used (e.g., when filling a form), simply because that's more practical than dealing with multiple names. When that's done, it's irrelevant if the omitted names are given or surnames, so it'd be OK to call them generically middle names.