According to the formalism d = v*t fourth dimension of space-time X₄ = i*c*t is spatial too. Time is not a fourth dimension of space-time. Material change i.e. motion run in a timeless space. Fundamental unit of numeric order t₀,t₁,t₂,...,t_n of material change is Planck time t_p . We measure numeric order of material change with clocks. Material change t_n-1 is "before" material change t_n equivalently as natural number n-1 is "before" natural number n. Numeric order of material change runs in a timeless 4D space and has no duration. Space-time is a timeless phenomenon.