If we spoken about Nobiliary titles that is basically because they are dictinctions granted by a king in vertue of his independent political and sovereign power transmitted to him by God through his Church to reward authentic nobles of his kingdom that they show their fidelity in God, in Roman Catholic Church and Pope and the Monarchic Institution for instance referred to the traditionnal spanish case
It remains necessary to clear that Noble people are only persons who receive these quality by blood in male line with inmmemorial Nobility at least since XV century, that is not a capricious date because this century indicates the end of medieval era.
If a noble Lady in spain marries a commoner their sons and daughters are commoners, but in the other side if a Noble gentleman marries a commoner, their children are Noble and this is like that, in vertue of the preference of male line established in the Code of SIETE PARTIDAS for XIII Century created by King Alfonso IX of Castilla, recovering a millenary Gothic tradition. (Democratic way of altering the order of the surnames is not admitted).
Besides in Spanish traditionnal Kingdom to inherit the title and the dignity of Head of the House, the Heir must be legitimate son of legitimate Roman Canonic marriage, because illegitimate sons if they were recognised by their father could only be gentlemen but not members of the Chivalric Orders, Nor inherit titles of Nobility.
It remains impossible to pretend to innovate medieval institutions applicating democratic rules, this is a nonsense, we don´t have to forget that nowdays the social condition of being noble and titled is not recpgnised in Democratic States of Europe in the side to obtain any privilege ( it is only an honorific and private matter ) so if we desire to be traditionnal we have to conserve those institutions with the rules created during the time that Sovereign kings ruled Spanish Country
The position of assuming these points of view are possible if we believe in God as the Creator of the Universe helped by is representant in earth who is the Roman Pope who legitims the King by sacrements giving to him Royal Sovereingnty who belongs to God .
So the essential basis about the Monarchy as a political, juridic religious and social sistem is:
* The King: in Tradituinnal Spanish Monarchy since it was created by Goths in V Century King was the Sovereign by the grace of God ( Spanish Kings before Ferdinand VII and this one died in 1833 based their authority in God without any participation of Commun people in SOVEREIGNTY wich is the concept that means that the hole powers of the State remain to the King but he is obliged in the same time to execute God Policy , protect the Roman Catholic Church, and be helped by Council of most important Nobles in order to rule the Kingdom respecting old laws wich are the expression of the anterior Kings, if not he is not the sovereign but a dictator and so not legitime.
And after H.M Ferdinand VII, died in 1833, the legitimate succession in the monarchy has been maintained in his principles and concepts during XIX, XX and XXI Centuries by his legal and legitimate successor according to 1713 act and 1805 act never abroged by any king , that was his brother H.M Carlos V (1833-1845 ), Dei Gratia and his successors: H.M Carlos VI Dei Gratia (1845-1861) son of the precedent, H.M Juan III Dei Gratia (1861-1868) brother of the precedent, because his eldest brother has no issue, H.M Carlos VII Dei Gratia (1868-1909) son of the precedent, H.M Jaime I Dei Gratia (1909-1931) son of the precedent, without issue, H.M Alfonso Carlos I Dei Gratia (1931-1936) uncle of Jaime I by paternal line, has no issue. Succeded firstly as Regent by H.R.H Prince Xavier de Bourbon Parme, who become in 1952 till 1975 H.M Javier I dei Gratia., succeded by his second son as Regent by H.R.H the Infant Sixto-Enrique de Bourbon Bourbon (1975 - ) protecting dinastic rights of their nephews HH RR.HH the Infants Carlos Javier, born in 1970, and his second brother Jaime de Bourbon Orange Nassau.
* The male preferent dinastic line becoming from H.R.H Infant Francisco de Bourbon Bourbon third brother of the King Ferdinand VII Dei Gratia, in male line, alive in 1936, was represented by Prince Alfonso de Bourbon Habsbourg so called Alfonso XIII by liberals and Constitutionnalists, he never recognised the legitimate Sovereign Kings by the grace of God so he was excluded of the traditionnal succession of the Spanish Throne, he and his descendence (Prince Juan) this was the rule of the Spanish monarchy by the Grace of God.for Princes of the Royal House who commited Trahison and Rebellion against the sovereign King.
* this was the samething for the succession of the Infant Don Carlos de Bourbon (born Bourbon Sicily) but naturalised spanish and member of the spanish Constitutionnal Royal Family since 1900 year and his son H.R.H Infant Alfonso de Bourbon, they didn´t want to recognise the traditionnal Monarchy sovereign by the Grace of God, nor his son Prince Carlos.
So came the dinastic branch of Bourbons of Parme and first dinastic rights come to H.R.H Prince Elias de Bourbon Duke of Parme D.G, who didn´t want to recognise H.M the King Alfonso Carlos I of Spain Dei Gratia,(1931-1936), nor his son H.R.H Prince Roberto de Bourbon, who become later Roberto II, Duke of Parme D.G
The Regent Javier de Bourbon could not alter capriciously the order of succession so the Regency was very long from 1936 to 1952 because it was necessary to propose the succession of the sovereign Monarchy to each Prince of the Royal House of Spain by male line and from the eldest to the youngest.
But all Princes mentionned above thought that it was better to recognise Liberal Revolution of 1833 imaginating that they could have more oportunities to have benefits from liberal Revolutionnary Parliaments, or from the fascist dictator at that time General Francisco Franco who called himself Head of the Spanish State
But when the turn becomes to the Regent Don Javier de Bourbon Bragance in 1952, he became H.M the King Don Javier I of Spain Dei Gratia as legitimate successor of the last Sovereign King of Spain Dei Gratia died in 1936 H.M the King Don Alfonso Carlos I of Spain Dei Gratia, absolutely independent from General Franco that king Don Javier I , D.G considered a traitor and a criminal.
King Don Javier recognised old laws called Fueros, in Guernica in 1950 and in Montserrat in 1951 and he recognised the principles and rules of the sacred Spanish Monarchy by the Grace of God asuming the Royal Soverignty and obeing absolutely the dinastic order in succession of the Crown according 1713 and 1805 (Only eldest males of the House of Bourbon can inherit the Crown, and females can not inherit Royal rights if they are males even if they belong to other dinastic branches far from the last King , that is the Semi Salic act, and if they are no males the eldest Royal female daughter of the last reigning King only if she is married with a Catholic Royal Prince can inherit the Spanish Crown).
These Laws were approoved and dictated by H.M the king Don Felipe V Dei Gratia (1713) and H.M the King Don Carlos IV Dei Gratia (1805) confirming at that time the only successorial system to inherit the Crown in Spain, and the Royal act of H.M the King Don Carlos III Dei Gratia of 1776 (preventing successors of the Crown marrying commoners and if they do it they loose their Royal rights to inherit the Crown for them and for all their descendance for ever), so he became in 1952 H.M the King Don Javier I of Spain dei Gratia.
All people must understand that those considerations are not an artifitial and symbolic establishment, because during XIX, and XX Centuries Carlist dinasty or Legitimate dinasty, represented by the Sovereign Kings dei Gratia mentionned above, fought against the liberals and Constitutionnals in four Civil Wars wich were terrible for the Country who was divided in Two parts with in one hand Monarchic armies of Requetés in front of Revolutionnary armies called Constitutionnalists o Liberals, from 1833 to 1840, then from 1846 1849, then from 1872 to 1876 and the last from 1936 to 1939, after a facist dictature was organised by a Traitor named Francisco Franco and his political successor Juan Carlos de Bourbon, who inherit the power from Franco after recognising his facist regime in a solemn ceremony, untill 1978, and after a democratic Constitution assuming popular sovereignty has been approoved in 1978 by Common People and political Revolutionnary organizations.
So The Revolutionnary Constitutionnalist regimes of the XIX Century (1833-1876) and XX Century dictatures as first dictature leaded by General Miguel Primo de Rivera (1921-1930) and after the Francisco Franco Fascist dictature (1939-1975) and then second fascist dictature (1975-1978) leaded by his successor Juan Carlos de Bourbon , and then the 1978 Democratic Constitution till nowdays in XXI Century who recognizes only the sovereignty of common People, have NO RELATION with the sacred and Sovereign Spanish Monarchy, ruled by kings in vertue of Royal Sovereignty by the Grace of God, even if they represent simbolic institutions nowdays, Monarchy can not be mixed or perverted or included in other political regimes, that is clear for everybody with a little of common sense.
So referring internal laws of royal Spanish dinasty, referring Nobility and titles and honorific treatments of Historical past of Spain, the democratic State has no authority to invent rules or laws created with democratic spirit in order to be applicated to Medieval Political simbolic institutions .
These are matters out of the competence of an a Democratic Regime so they have to continue to be ruled according their internal and traditionnal Monarchic laws, in a symbolic way without any privilege in Democratic State, and because of this reason the Heads of Noble Houses of the old Kingdom of Spain Dei Gratia, we have to insist maintainig our independence and preserving the transmission of our titles and noble condition obeing only to traditionnal Monarchic Law.
So in conclusion I can affirm properly that nowdays in XXI Century in 2008 Year, Juan Carlos de Bourbon is the Head of the Democratic Constitutionnal Spanish State (created in 1978 organised according to Sovereignty of people)
In an other hand H.R.H the Infant Don Sixto Enrique de Bourbon and Bourbon is the Regent of Spain Dei Gratia, obeing Dinastic rules (1713 law, 1776 Law, 1805 Law) of Traditionnal Spanish Monarchy in this historic and symbolic side.
And there are too, in a social outlook, Noble Titled Families that in a symbolic and private social side are dukes, marquesses, earls, viscounts, barons, hidalgos (not titled nobility) and Knights of the Military Orders of Chivalry (recognised only by Roman Pope for spanish Nobility), obliged by tradition to preserve their nature and the history of their lignages and honorific distinctions that it constitute too the historical Legacy of the Country, absolutely independent about the State in the preservation and transmission of titles of Nobility and Nobiliary conditions to inherit their symbolic condition obeing only traditionnal Law of Spanish Sovereign Monarchy.