Simultaneum (scil. Religionis Exercitium) is a term which in Europe designates, in its general bearing, the religious services common to churches or denominations having diverse creeds, and which has particular reference to the employment in common of certain religious arrangements and institutions.
The denial of a churchly character by Romanism to any but the Papal Church renders a simultaneum impossible of that assumption; but the Peace of Westphalia in 1648 insured to the Evangelicals both that character sand the resultant rights of worship. The progress of the new Church, however, was irregular, in some places being much more vigorous and rapid than in others, so that the relations existing between Romanists and Protestants were very diverse; and it was thought necessary to provide legal prescriptions for the exercise of a common worship. These prescriptions erected a barrier against religious persecution on the part of a sovereign prince, but they also suggested the denial of religious privileges to certain parties, since the status of the year 1624 was made the condition for granting or refusing the free exercise of religion they who had then enjoyed it being held to be entitled to a continuance of the privilege, while others were generally, though not always, judged to have no claim to its enjoyment. These regulations were intended to settle the case as between Romanists and Protestants. A different arrangement regulated the affairs of the Lutheran and the Reformed parties, so that the condition of the churches at the conclusion of the Peace of Westphalia was made the basis of their future relations.
The admissibility of a simultaneum was much debated in Germany, until the recess of the diet resolved, Feb. 25, 1803, § 63, that "the exercise of religion as hitherto practiced in any country shall be protected against all interference and interruption; especially shall the possession and undisturbed enjoyment of its separate ecclesiastical property, including the school fund, be insured to each religion according to the direction as of the Peace of Westphalia. The sovereign may, however, tolerate the adherents of other religions and allow them the exercise of all civil rights." The simultaneum does not affect the dogmatic relations of the several churches. The Church of Rome still regards Protestants as heretics and schismatics, and refuses to recognize the validity of their services; and the different sections of Protestantism have frequently maintained towards each other an attitude no less hostile. Circumstances, however, have done much to bring about a state of things in which the spirit of a simultaneum is measurably realized. Legislation has done much in this regard, and the felt need of fraternal relations has not been least among the influences at work.
When the simultaneum has been fixed by special treaties, it must be judged in accordance with their terms, otherwise general principles must determine. The State does not assume the right to ordain the observance of the usages belonging to one religious community by another and different community on general grounds; but it may extend the benefits of institutions enjoyed by any community to others as well, e.g. when civil functions have been intrusted to the clergy of a particular Church, or when but a single burial ground is available for any community.
It is reported (Prot. Kichen Zeitung, 1854, No. 5, p. 102) that a very peculiar simultaneum existed at Guldenstadt, in Osnaburg, during two hundred years prior to 1850. A Roman Catholic and an Evangelical congregation had a common house of worship, and employed in common a Romish priest and a Protestant clerk. The priest and Romanists began the service with the Introit, after which the Evangelicals chanted the Kyrie Eleison. Alternate chantings and readings followed, until the offering of the mass, in which the Evangelicals took no part. A sermon was preached to both parties in common, and was usually followed by the singing of an appropriate evangelical hymn. One instance is mentioned in which a sermon assailing the Lutheran Confession of Faith was followed by the singing of Luther's hymn, "Eine feste Burg," etc.
In America what are called "Union Services" are frequently held in a church used in common by several denominations. In such cases the services are some times of a mixed character; at other times the different denominational services are held alternately.
On the general subject, see Intsrum. Pacis Osnabrug.; Putter, Geist des westph. Friedens (Gott. 1795); Enders, Diss. de Pactorum, Hildens. in Confirm. Comm. Cathol. Doctr. circa Simultaneum Efficacia (1765, 1771); and in Schmidt, Thesaur. Juris Eccl. tom. 5, Nos. 7, 8, p. 257 sq., 326 sq.; Durr, Diss. de eo, quod Justum est circa Jus Reform. in Territor. Oppignerato, etc. (Mogunt, 1760, and in Schmidt, loc. cit.); Schottl, Gegenseit. Gemeinsch. in Cultushandl. zw. Katholiken u. Akathol. etc. (Regensb. 1853). Comp. also the Austrian law of Jan. 30, 1849; Circular d. Consist. zu Detmold, July 27, 1857; Von Moser, in Allg. Kirchenbl. f. d. evangel. Deutschl. 1857, p. 372, etc.