Quantity 
Name 
Symbol 

1

length 
meter

m

2

mass 
kilogram

kg

3

time 
second

s

4

electric current 
Ampere

A

5

thermodynamic temperature 
Kelvin

K

6

amount of substance 
mole

mol

7

luminous intensity 
candela

cd

These Basic Units are currently considered the most fundamental concepts in physics. This is critical:
Each SI Basic Unit is a defined concept.
The definitions of these 7 Basic Units are considered fundamental and are the building blocks of modern physics. This is critical:
Basic Units are used to derive
all other concepts in physics.
The other concepts are called Derived Units.
"Force" is one common example of a Derived Unit. The unit of force is called the "Newton" (N = m kg/s^{2}). This Derived Unit derives its meaning from the beginning definitions of the Basic Units: mass, length and time. Mathematically, the "Newton" is a function of: mass, length and time:
Perhaps the simplest Derived Unit  in currently accepted physics  is that of "motion." In currently accepted physics, motion is described in terms of "speed" or "velocity." The units for both are: length/time. In other words the concepts "speed" and "velocity"  in currently accepted physics  are Derived Units. They derive their meaning from the original definitions of the SI Basic Units: length and time. This is critical:
Mathematically, "speed" and "velocity"
are functions of: length and time:
Einstein's Special and General theories of Relativity are considered cornerstones for modern physics. The Lorentz transformations  the key equations central to Relativity  are usually written in the form:
This is critical:
The first and fourth equations effectively
redefine the Basic Units: length and time.
However, note there is a Derived Unit  velocity  in the denominators of both expressions. This is critical:
Mathematically, these expressions state that:
length is a function of velocity;
and time is a function of velocity:
Relativity also states that mass is a function of velocity with the expression:
Mathematically, this expression effectively states that: mass is a function of length and time:
Summary of Logical Argument:
 SI Basic Units are defined
 SI Derived Units derive their meaning from the definitions of the SI Basic Units
 Mass, Length, and Time are 3 of the 7 SI Basic Units
 Velocity is a SI Derived Unit  deriving its meaning from the beginning definitions of (SI) Length and (SI) Time
 Relativity defines (SI) Time as a function of (SI) velocity
 Relativity defines (SI) Length as a function of (SI) velocity
 Relativity defines (SI) Mass as a function of (SI) velocity
 Therefore, (SI) velocity is defined as a function of (SI) time and (SI) time is defined as a function of (SI) velocity.
 Therefore, (SI) velocity is defined as a function of (SI) length and (SI) length is defined as a function of (SI) velocity.
 Points 8 & 9 are circular definitions, therefore, using SI Basic Units, Relativity is illogical. This aspect of Relativity is unresolvable. Relativity can not be used as a foundation for physics with this problem.
 It is also illogical to define one SI Basic Unit  Mass  as a function of two other SI Basic Units: Length and Time.
Let me emphasize, I am not questioning the physical effects that have been observed that supposedly support Relativity, or that they are actual phenomena of nature. The point is, Relativity is not a logically correct way to describe these physical observations. Relativity was developed to answer the question of how to add velocities and not exceed the speed of light. Another method of solving this centuryold question is needed that does not use the illogical circular definitions within Relativity. The Speed of Light Definition of Time does just that.
To summarize, instead of measuring all motions with our historical standard of motion  the sun's apparent motion for an earthbound observer as it crosses the sky  and then correcting this geocentric reference frame for all other observers in other reference frames  using Relativity  scientists must redefine time to be the fastest known motion  the speed of light in free space  thus allowing one standard of motion to be used in all reference frames without need for a correction factor.
