JUDGMENT : It is a case wherein the defendants 1 and 2, the co-owners, claimed adverse title based on two documents of ouster Exts.B1 and B2. Ext.B1 is the demand notice for partition of the year 1979 issued by the plaintiff to the 5th defendant, to which, the 5th defendant replied under Ext.B2 denying right, title and interest of the plaintiff over the property and claimed exclusive right, title and interest over the property. But no suit for partition or for any declaration instituted within a period of twelve years from the date of receipt of Ext.B2 reply. Ext.B2 reply was raised as an act of 'ouster' asserting exclusive right, title and interest by the 5th defendant over the property against the co-ownership right claimed by the plaintiff. 2. The essential questions came up for consideration in this appeal are : (1) What actually amounts to an act of “ouster” in the matter of co-ownership property and claim of perfection of adverse title ? (2) Whether there would be a valid 'ouster', unless coupled with disturbance of possession from that of a co-ownership to adverse ? (3) Whether such exclusive possession in furtherance of the ouster should be maintained for the required period of twelve years so as to perfect title by adverse possession ? (4) What would be the legal impact of continuance of undisturbed possession of co-ownership property after the act of 'ouster' and whether there is any change in the legal position when there is subsequent interference to the possession during the period of inchoate right by the co-owner against whom an act of 'ouster' is imposed ? 3. Issuance of a demand notice for partition which was not pursued further for a long period more than twelve years was taken into consideration by the Apex Court in Govindammal v. R.Perumal Chettiar and Ors ( AIR 2007 SC 204 ) so as to ascertain whether it would constitute an 'ouster' and held that it is not sufficient to show that the co-sharer has lost her right by adverse possession simply because she gave notice claiming partition of the suit properties and possession and did not pursue the matter further. It was further held in that decision that the person setting off ouster is bound to show that he did set up an adverse or independent title during the period which was beyond the statutory period of twelve years. But in that case, there was no express denial by issuing a reply notice in writing. What is involved in that case is that the person, who had issued notice demanding partition not pursued further for a long period of more than twelve years and the question came up for consideration was whether it would constitute an 'ouster' for perfecting title by adverse possession. 4. In the instant case, there is an express denial of right, title and interest of plaintiff by the 5th defendant by issuing a reply notice, Ext.B2. No suit was filed for partition for a long period of more than twelve years after the receipt of Ext.B2. Hence Ext.B2 raised as an 'ouster' against the co-owner, the plaintiff. But the plaintiff was in actual possession of the property even after the issuance of Ext.B1 demand for partition and Ext.B2 reply issued denying his right, title and interest over the property. There is no disturbance to the possession held by the plaintiff over the property even after the issuance of Exts.B1 and B2. But the plaintiff continued his possession over the property by residing in the house situated therein. It is the well established principle that possession held by one of the co-owners should be and must be for and on behalf of all co-owners and there cannot be any acquisition of adverse title unless there is clear 'ouster'. The expression 'ouster' stands for an assertion of right, title or interest over the property in derogation of the other persons having title over the property including a co-owner and interested persons thereof. In order to bring out an 'ouster', it should be a one openly expressing the animus to hold the property in derogation of the other co-owner and in the case of permissive possession, against the owner. The co-owner who claims adverse title has to prove ouster of other co-owner by an open assertion to the knowledge of that co-owner expressing and asserting his animus to hold the property in derogation of right, title or interest of that co-owner. The co-owner who claims adverse title has to prove ouster of other co-owner by an open assertion to the knowledge of that co-owner expressing and asserting his animus to hold the property in derogation of right, title or interest of that co-owner. The animus to hold the property stands for exclusive possession of property and animus to hold the same exclusively as against the other co-owner. The ouster must qualify the requirement of the necessary animus to oust the co-owner from possession of the property in derogation of his interest and it must be maintained till perfection of title by adverse possession by completion of required period of twelve years with the necessary classical requirement nec vi nec clam nec precario. Any interruption or disturbance to the possession within the required period of twelve years would terminate the assertion done earlier. Hence the expression 'ouster' should be understood as an assertion expressing the hostile animus to hold the property against the other co-owner involving change of nature of possession to an adverse from that of the co-ownership possession or permissive possession as the case may be. In order to bring out an effective 'ouster' as against a co-owner, a mere assertion of right, title or interest in derogation of the other co-owner, or against the original owner in the case of permissive possession, is not sufficient. To put it short, 'ouster' stands for change of nature of possession of property from permissive to adverse by asserting exclusive right, title or interest in derogation of other person. Necessarily, the factual scenario regarding actual possession and symbolic possession will have its own role to play in adjudging a valid 'ouster' as against a co-owner or against the owner in the case of permissive possession. Unless the 'ouster' was accompanied by disturbance of possession from that of co-ownership or permissive to exclusive possession and maintenance of the same openly with the required animus for the required period, there cannot be an adverse title as against the co-owner or interested person. The animus to hold the property in derogation of the right of other co-owner with notice is the essence of adverse possession and acquisition of adverse title. There need not be any notice in writing or express notice, but the act of 'ouster' should be capable of giving notice regarding open assertion and ouster. The animus to hold the property in derogation of the right of other co-owner with notice is the essence of adverse possession and acquisition of adverse title. There need not be any notice in writing or express notice, but the act of 'ouster' should be capable of giving notice regarding open assertion and ouster. If the person who was ousted subsequently came into possession of property or continued his possession as a co-owner without any disturbance even after the assertion of adverse title by way of ouster, the ouster can only be considered as incomplete and ineffective. In other words, there cannot be an effective 'ouster' unless the possession over the property altered and changed into an adverse possession with the required animus as against the other co-owner. Any alteration or interference to the possession subsequent to the ouster during the period of inchoate right or continuance of earlier co-ownership possession without any disturbance would take away the act of 'ouster', if any employed and would make the 'ouster' invalid and ineffective. 5. When a co-owner is in actual possession of the property, though his possession refers to possession of co-ownership for and on behalf of all co-owners, an act of ouster done by him expressing his intention to hold the possession exclusively for him with the necessary animus and notice to other co-owners would itself change the character of his possession into an adverse one, without any further act, either physical or otherwise and it would amount to an 'ouster' provided that it should be maintained for the required period so as to get it perfected by adverse title. But, the legal position would be different, if the possession was actually held by the other co-owner against whom the act of ouster was raised, wherein, a clear act of ousting possession of that co-owner in derogation of his interest must be established in order to bring out an effective 'ouster'. In the instant case, the plaintiff was in actual possession of the property even after the issuance of Exts.B1 and B2 documents and the alleged ouster under Ext.B2 document and continued his possession as a co-owner till the date of suit. Hence there cannot be an 'ouster' by a mere assertion unless coupled with diversion of possession. The concurrent finding rendered by both the courts below rejecting the claim of 'ouster' hence deserves no interference. Hence there cannot be an 'ouster' by a mere assertion unless coupled with diversion of possession. The concurrent finding rendered by both the courts below rejecting the claim of 'ouster' hence deserves no interference. No other substantial question of law is involved. The appeal fails, dismissed. No costs.