The offer must be made in order to create legal relations otherwise there will be an agreement. If an offer does not give rise to legal obligations between the parties it is not a valid offer in the eye of law. In business transactions there is a presumption that the parties propose to make legal relationships. For example a person invite to another person to diner if the other person accepts the invitation then it is not any legal agreement between the parties it is social agreement.
An offer must be definite and clear. If the terms of an offer are not definite and clear it cannot be called a valid offer. If such offer is accepted it cannot create a binding contract. An agreement to agree in future is not a contract because the terms of an agreement are not clear. A person has two motorbikes. He offers to another person to sell his one bike for a certain price then it is not a legal and valid offer because there is an ambiguity in the offer that which motorcycle the person wants to sell. There is a difference between the offer and invitation of offer. Sometime people offer the invitation for the sale.
An offer must be definite and clear. If the terms of an offer are not definite and clear it cannot be called a valid offer. If such offer is accepted it cannot create a binding contract. An agreement to agree in future is not a contract because the terms of an agreement are not clear. A person has two motorbikes. He offers to another person to sell his one bike for a certain price then it is not a legal and valid offer because there is an ambiguity in the offer that which motorcycle the person wants to sell. There is a difference between the offer and invitation of offer. Sometime people offer the invitation for the sale.