Difference Between Constant and Control

Empirical studies and experimentation are some of the major components of science without which valid scientific knowledge cannot be acquired. To find out the cause of a particular phenomenon, a variety of experiments needs to be conducted.

Experiments are all about observing, analysing and predicting changes. The elements that change in an experiment are known as variables. Constant and Control are two very important variables that are used in an experiment.

Constant vs Control

The main difference between Constant and Control is that a constant variable does not change throughout an experiment. A control variable, on the other hand, can change but is deliberately kept constant to isolate the interrelation between an independent variable and a dependent variable.

Constant vs Control

A Constant variable is one that does not go through any change under any circumstances, neither between nor during experiments.

A Control variable, on the other hand, is one that has the potential to change but is deliberately kept constant by the conductor of the experiment so that the interrelation between an independent variable and a dependent variable can be isolated.


Comparison Table Between Constant and Control (in Tabular Form)

Parameter of ComparisonConstantControl
Used inScientific Experiments and Algebraic Expressions.Scientific Experiments.
ValueDoes not change in any situation.Can change but is deliberately kept unchanged.
SignificanceIt is of primary interest.Act as a third factor.
GraphNot depicted on the graph.Can be graphed for checking that all other conditions except those concerning the experiment are unchanged.
PurposeMust be recorded for the reproduction of the experiment.Helps in showing the interrelation between an independent variable and a dependent variable.


What is Constant?

It is a variable in an experiment; the value of which once assigned can be changed, neither during nor in between experiments. However, as the value of a constant does not change, it is often not considered a variable at all.

In an experiment, a variety of natural properties or forces are taken as constants. For example; to observe the changes that a plant undergoes due to the effects of different kinds of lights, one needs to take factors like soil quality and watering etc. as constants.

However in certain cases, a particular factor, force or property is taken as constant merely for the sake of an experiment. If observed in real life, such factors, forces or properties can undergo considerable changes due to the influence of certain external factors or under certain circumstances.

In this context, one can take the example of the boiling point of water which changes according to the acceleration and altitude of an area. This happens because of a decrease in gravity with a corresponding increase in distance from the earth.

In mathematical expressions, the term constant is used to refer to a number that exists all by itself. This is because the value of such a number never changes. For example:

In expression 3x+4, the value of the term ‘3x’ varies with the value of x. But the value of the term 4 does not change. It follows that in the expression 3x+4, the term that can be referred to as a constant is 4.


What is Control?

It is a variable that has the potential to change but is deliberately kept constant so that it becomes easier to depict the interrelation between independent and dependent variables. For example:

In an experiment for observing and analysing the effects of different forms of light on the growth of a plant, one needs to keep the temperature same for all the plants used in the experiment. This is because the focus is on how a plant reacts to different forms of light and not how it reacts to different temperatures. Thus, the amount of temperature in this experiment is a control variable as it is an element that needs to be controlled.

Similarly, the person experimenting also needs to be careful with the amount of water he is giving to each plant. This is because, if by any chance one of the plant is given more water than the other plants, it would not be possible to comprehend the reason behind the growth of that plant. One would fail to know if the reason behind the growth of that plant was a form of light or excess water.

In a science experiment, a control variable is not of any primary importance. Rather it acts a third factor. But it is still important for an experiment. This is because it helps in comparing other variables that may have contributed to a particular outcome of the experiment as all variables pertinent to the experiment are kept the same or under control by the person experimenting.

While graphing an experiment, the independent variable is represented by the x-axis while the y-axis represents the dependent variable. But the controlled variables are not depicted on a graph as they are not supposed to change. But they can be depicted on a graph to make sure that all other variables except independent and dependent variables should not change.

For example; after plotting the growth of plants in comparison to the lights received on a graph, one can also check if all the plants received the same amount of temperature or water or not. If any variation is found, one needs to re-check the set up of their experiment.

Main Differences Between Constant and Control

  1. Both Constant and Control are important for a scientific experiment. But the constant variable is of primary importance to an experiment. While, the control variable constitutes the third factor of an experiment.
  2. The value of constant does not vary in any situation. While the value of control has the potential to change.
  3. While plotting the graph of an experiment, the constant variable is not depicted on the graph. However, a control variable can be graphed for verifying the fact that all other conditions except the independent and dependent variables are the same.
  4. While experimenting, the constant must be recorded so that the experiment can be reproduced. Whereas, a control variable is used for a clear depiction of the correlation between the dependent and independent variables.
  5. A control variable is only used in scientific experiments. Whereas a constant is also used in mathematical or algebraic expressions.



While experimenting, people often get confused between Constant and Control. This happens because the value of a Control variable is not changed in an experiment despite it having a potentiality to change.

Nonetheless, both Constant and Control are integral to an experiment as they determine the outcomes of the experiment. But between these two, constant variable is of primary interest to the experiment and cannot be eliminated under any circumstances. But the value of a control can be determined or it can be eliminated.


  1. http://www.businessdictionary.com/definition/constant-variable.html
  2. https://www.statisticshowto.com/control-variable/
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