"Investment banks" create loan agreements that cater to the needs of the investors whose funds they attempt to attract; "investors" are always sophisticated and accredited organizations not subject to bank regulatory supervision and the need to cater to the public trust. Investment banking activities are supervised by the SEC and their main focus is on whether the correct or proper disclosures are made to the parties who provide the funds.
When you have a financial crisis, it is quite common that we search for various sources of funding. Though we might have helped our friends, they cannot do much when we are in need due to several reasons. If we maintain good credit score, then the best source for funding your needs is taking a loan that you can get through loan agreement process.
The loan agreements originated by commercial banks, savings banks, finance companies, insurance organizations, and investment banks are very different from each other and all feed a different purpose. "Commercial banks" and "Savings banks," because they accept deposits and benefit from FDIC insurance, generate loans that incorporate the concepts of the "public trust." Prior to interstate banking, that "public trust" was easily measured by State bank regulators who could see how local deposits were used to fund the working capital needs of local industry and businesses, and the benefits associated with those organization's employment.
Loan agreements, like any contract, reflect an "offer," the "acceptance of the offer," "consideration," and can only involve situations that are "legal" (a term loan agreement involving heroin drug sales is not "legal"). Loan agreements are documented via their commitment letters, agreements that reflect the understandings reached between the involved parties, a promissory note, and a collateral agreement (such as a mortgage or a personal guarantee). Loan agreements offered by regulated banks are different from those that are offered by finance companies in that banks receive a "banking charter" granted as a privilege and involving the "public trust."