Well, no. Oughts also apply also to attitudes. One ought to desire that which one really needs. If morality is objective (as I believe it is) then it cannot be otherwise.
"It is the fact that man's life, the factual life requirements, are both the standard and the purpose." ?
Do you mean man's factual needs are the standards necessary to live a human life? Objective (moral) standards, as opposed to arbitrary standards, e.g., the length of a meter, are a priori knowledge. A priori knowledge, usually inferred from self-evident premises, is acquired through reason rather than observation. Example:
Man is naturally a social creature.
Social creatures live in organized communities.
Therefore, man needs to live in organized communities.
If true then Objectivism leads to societal chaos requiring the use of governmental force to impose order.
If every thinker defines human nature then no one defines human nature for others.
All men are a thinking animals.
Every man defines his human nature.
No man defines man's nature for all men.
? If true than morality cannot be objective and we're back to the existence of a priori knowledge.
Are not conclusions reached logically rather than empirically a priori knowledge? Of course they are. One does not observe the rules of logic. The rules of logic appeal to reason and the first principles for their validity.
Yes, it is the facts of reality related to man's nature that make morality necessary. An objective moral value is some aspect of reality in relation to man's life, e.g., man needs food to live, then he ought to obtain food if he wants to live. The moral principle that man should eat things that are good for him and support his life is derived from these facts inductively. Moral principles are inductive in nature as are all principles.
Life is the standard of morality because it is the goal of morality. It is the purpose. People always ask "what's the purpose of life?". The answer is life. Life is an end in itself, to be pursued for its own sake and not as a means to another value. It is the source of values. Therefore, logically, it must be the standard of morality, i.e., every action, choice, and value must be judged in relation to it.
You simply can not, in logic, divorce morality from life. Life is the only thing that makes values possible and the only thing that makes them necessary and since no one is born knowing what is good for him or bad, then he needs to discover the values that his life requires. He does not invent them or decide them, he discovers them. They are not determined by society, gods, governments, kings, councils, authorities, religious gurus, or your parents. That's why if you ask an Objectivist where his morality comes from if there is no god, he will say it comes from existence because that's where all knowledge comes from. There's no shortcut. You can't cut corners. Others are not the source of knowledge. Books are not the source of knowledge. The Koran is not the source of knowledge. Ayn Rand, John Locke, Plato, Aristotle, Freud, and your professor in college is not the source of knowledge. Reality is.
Now I understand your reference to apriori knowledge. Objectivism rejects the Analytic-Synthetic dichotomy in principle and in all its various forms and offshoots such as the Necessary-Contingent dichotomy and the Rationalism-Empiricism dichotomy and with good reason. It is the result of a flawed understanding of concepts. It treats concepts as shorthand tags for their definitions. In other words, a concept's meaning is its definition which is arbitrarily constructed. This cleaves a concept from reality and makes it a social construct.
I hold to the Objective Theory of Concepts which states that concepts are mental integration of concretes that we perceive directly by looking at reality. A concept's meaning is the concretes that it subsumes. Definitions name the concretes that the concept subsumes in terms of their essence or the essential characteristics of the particular concretes. The purpose of a definition is to tie the meaning of the concept to reality and to differentiate those concretes it subsumes from all others. All of the other characteristics are part of the meaning of the concept including things we have not learned yet learned but they are not included in the definition because this would defeat the purpose of a definition. There is no difference between those characteristics that are included in the definition and those that are not. There is no knowledge that we can gather apriori from applying logic to those characteristics included in the definition as opposed to those synthetic truths that come from empirical experience. There is only logic applied to observed facts. A concept's meaning is its referents and everything about them. Thus the concept "man" means all men and everything about them, not just rationality and animality.
I highly recommend that you read An Introduction to Objectivist Epistemology for more. I'm sorry that I couldn't provide a more detailed, point-by-point response. My busy season has started early this year and I just don't have the time to devote. Truth be known, this will probably be my last post on these forums. I just don't have the time anymore and frankly, I find this place depressing and I don't like being here. I start to lose hope for the future when I come here and read the posts. I don't want to be depressed, I want to enjoy my life and be happy.