The actual rule is in Section 179 of the Tax Code. The easier-to-read version is in IRS Publication 946:
What Property Qualifies?
To qualify for the section 179 deduction, your property must meet all the following requirements.
It must be eligible property.
It must be acquired for business use.
It must have been acquired by purchase.
It must not be property described later under What Property Does Not Qualify .
https://www.irs.gov/publications/p946#idm[phone number removed]952
