Transfer by Ostensible Owner (Section 41, Transfer of Property Act, 1882):

Section 41 deals with transfers made by an 'ostensible owner'. An ostensible owner is not the real owner of the property but has been allowed by the real owner to appear as such to the world. This appearance of ownership is created by the express or implied consent of the real owner. The doctrine is based on the principle of estoppel, where if a person allows another to hold themselves out as the owner of their property, they cannot later deny that person's authority to transfer it to a bona fide purchaser.

Conditions for a valid transfer by an ostensible owner:

1. Ostensible Ownership: The transferor must be the ostensible owner of the immovable property.
2. Consent of Real Owner: The real owner must have given their express or implied consent for the transferor to hold themselves out as the owner. This consent implies that the real owner has consciously allowed the appearance of ownership.
3. Good Faith of Transferee: The transferee must have acted in good faith, believing the ostensible owner to be the true owner.
4. Reasonable Care: The transferee must have taken reasonable care to ascertain that the transferor had the power to transfer the property. This implies making necessary inquiries that a prudent person would make.
5. Consideration: The transfer must be for consideration.

If these conditions are met, the transfer by the ostensible owner is valid and cannot be set aside by the real owner. The real owner is estopped from asserting their title against the bona fide transferee. The rationale is to protect innocent third parties who rely on the apparent ownership created by the real owner's conduct.

Transfer by Unauthorised Person Who Subsequently Acquires Interest (Section 43, Transfer of Property Act, 1882 - Doctrine of Feeding the Grant by Estoppel):

Section 43 embodies the doctrine of 'feeding the grant by estoppel' or 'estoppel by deed'. It applies when a person fraudulently or erroneously represents that they are authorised to transfer certain immovable property and professes to transfer it for consideration, but at the time of transfer, they do not have the interest in the property. If, subsequently, the transferor acquires any interest in that property, the transfer, at the option of the transferee, operates on the interest so acquired.

Conditions for the application of Section 43:

1. Fraudulent or Erroneous Representation: The transferor must have made a representation (fraudulently or erroneously) that they have an interest in the property and are authorised to transfer it.
2. Professed Transfer for Consideration: The transferor must have professed to transfer the property for consideration.
3. Lack of Interest at Transfer: At the time of the transfer, the transferor must not have had the interest they professed to transfer.
4. Subsequent Acquisition of Interest: The transferor must subsequently acquire the interest in the property.
5. Transferee's Option: The transferee must not have rescinded the contract and must exercise their option to enforce the transfer against the subsequently acquired interest.

Effect: When these conditions are met, the subsequently acquired interest of the transferor 'feeds' the earlier defective grant, making the transfer valid from the date the interest is acquired. The transferor is estopped from denying the validity of the earlier transfer. This doctrine prevents a person from taking advantage of their own fraud or error and ensures that a promise made for consideration is upheld once the means to fulfill it become available to the promisor. It protects the transferee who acted on the transferor's representation.