Should there be a law defining human life, at what point it begins; Sperm, egg, conception, cognition?

I believe cognition for only when there is absence of brain activity do we consider someone legally dead. Therefore logically only when there is brain activity should some one be considered legally alive.
At one time the Catholic Church believed that every component of the fertilization process to be sacred. By this standard anti-abortionists would find themselves protesting outside of peek booths, or places that sold condems for the seman spilled would be murder. Sounds rediculous doesn't it? But the standard of 'I think therefore I am' Cognition equals life would on the contrary allow for abortions up to the mid part of second trimester when brain activity begins in the fetus, but afterwards it would be considered killing not contreception.
I know that not all my liberal friends will agree, but I think that law needs to be black and white on this, and this is a viable solution.
I am saying cognition not quality of cognition.
This is an important topic and I am glad you brought it up. I think your 'cognition' is not as black and white as you belive. Depending on person's background, his or her opinion on this will vary greatly. Therefore, finding consensus on this topic will be diffilcult if not impossible.

Personally, I have to heed to a practical answer than an emotional or religious answer. 20 weeks after conception
It depends on the state laws. In the state of Illinois, life begins at conception.


Answers:
This is a really good question and one of the hardest to answer because there is no real answer. You present an interesting idea but I am not sure that a black and white definition beyond what the Supreme Court has decided could or will ever be made. How do we balance science, religion, right to life, and freedom of choice while preserving the rights of all involved? We cannot. Any 'solution' will be objectionable to at least one of the groups - just as it is now. A fetus seems to only have rights and recognition of its life when an act of violence is committed against the mother results in its unwanted death or when it survives past the date when it can be legally aborted. Pure science recognizes fertilization of the egg as the beginning of life. Religion and right to life groups recognize the sanctity of the fetus throughout. Pro-choice is supported by the law of the land - a law which in all likelihood will never be repealed. So, I feel that we will continue on as we are now - not with a black and white law but only in a gray and hazy situation. . .
If you were a vegetable, would you want somebody to pull your plug?

You have 2 versions of life:

scientific: unicellular and multicellular (CHON, Carbon-Hidrogen-Oxigen-Nitroge...
philosophical: 5 senses (6 senses if you count perception)

which one of the 2 are you going to use?
I don't agree with that because you may have brain activity, but you don't necessarily have awareness of any kind. Even so-called 'vegetables' have brain activity. It it a sin to give them medication that will shut their system down if that's what they wanted? If however it is shown that the brain activity is connected to pain receptors, I think that abortion should definitely not be used in that case.

Edit:
Since I know now that you mean awareness and actually thinking, I would agree with that.
There already is a law that protects life.God's law,& it starts at conception!
I agree with you! The soul is what we are, not something we have. The body is something we have and use, not what we are. I think that when the fetus has brainwaves, which indicates that he/she is actually thinking, that is an excellent indication that the soul has chosen to use this particular body for however long it chooses to. I believe that you are right in stating that the law in this matter needs to be standardized.